Purification of the Spliced Leader Ribonucleoprotein Particle
from Leptomonas collosoma Revealed the Existence of an Sm
Protein in Trypanosomes
CLONING THE SmE HOMOLOGUE*
Igor
Goncharov,
Zsofia
Palfi
,
Albrecht
Bindereif
, and
Shulamit
Michaeli§
From the Department of Biological Chemistry, The Weizmann Institute
of Science, Rehovot, Israel 76100 and the
Institut
für Biochemie, Humboldt-Universität/Charité
Monbijou-Strasse 2a, D-10117 Berlin, Germany
 |
ABSTRACT |
Trans-splicing in trypanosomes
involves the addition of a common spliced leader (SL) sequence, which
is derived from a small RNA, the SL RNA, to all mRNA precursors.
The SL RNA is present in the cell in the form of a ribonucleoprotein,
the SL RNP. Using conventional chromatography and affinity selection
with 2'-O-methylated RNA oligonucleotides at high ionic
strength, five proteins of 70, 16, 13, 12, and 8 kDa were co-selected
with the SL RNA from Leptomonas collosoma, representing the
SL RNP core particle. Under conditions of lower ionic strength,
additional proteins of 28 and 20 kDa were revealed. On the basis of
peptide sequences, the gene coding for a protein with a predicted
molecular weight of 11.9 kDa was cloned and identified as homologue of
the cis-spliceosomal SmE. The protein carries the Sm motifs
1 and 2 characteristic of Sm antigens that bind to all known
cis-spliceosomal uridylic acid-rich small nuclear RNAs (U
snRNAs), suggesting the existence of Sm proteins in trypanosomes. This
finding is of special interest because trypanosome snRNPs are the only
snRNPs examined to date that are not recognized by anti-Sm antibodies.
Because of the early divergence of trypanosomes from the eukaryotic
lineage, the trypanosome SmE protein represents one of the primordial
Sm proteins in nature.
 |
INTRODUCTION |
In trypanosomes all mRNAs are processed by
trans-splicing, which joins a common spliced leader
(SL)1 derived from the SL RNA
to polycistronic pre-mRNAs (1, 2). The SL RNA fulfills a dual
function, both recruiting splicing co-factors and serving as a
substrate for splicing. In analogy to cis-splicing,
trans-splicing requires the participation of U snRNPs.
Initial studies identified U2, U4, and U6 snRNAs in trypanosomes (3),
and their essential role in trans-splicing was demonstrated
(4). Only recently, the trypanosome U5 homologue was identified (5, 6),
but no U1 homologue has been revealed so far (3).
The trypanosome U snRNAs are generally smaller and show differences
from their cis-spliceosomal counterparts (3, 7). Another
unique property of the trypanosomatid snRNAs is that they possess a
divergent Sm site. In other eukaryotes, the Sm site constitutes the
binding site for the common Sm proteins (8) that are recognized by
anti-Sm antibodies present in autoimmune patients (9). Surprisingly, so
far, the trypanosome snRNPs represent the only exception in that they
are not recognized by these antibodies, suggesting unique properties of
the trypanosome core proteins (10, 11). Five core snRNP proteins were
identified in Trypanosoma brucei ranging in size from 15 to
8.5 kDa, which are shared among all trans-spliceosomal
snRNPs, including the SL, U2, U4/U6 (11), and U5 RNP (12).
Recent studies in both mammalian and yeast systems have demonstrated
that all the known Sm proteins possess homology in two regions that
were termed Sm motifs 1 and 2 (13-15). The Sm motifs are also
conserved in all putative homologues including plant and yeast
(13-15). This suggests that Sm proteins may have arisen from a single
common ancestor. Recently, Sm-like proteins that do not belong to the
canonical core proteins were also revealed, and one of them was
identified as a U6-specific protein (14).
Very little is known about snRNP proteins in trypanosomes. The two
trypanosome proteins that have been identified so far are the
U2-specific 40 kDa, the human homologue of U2A' (16) and the
U5-specific PRP8/p220 homologue (12). Interestingly, not all the amino
acid positions critical for PRP8 function are conserved in the
trypanosome protein p277, suggesting that certain differences exist
between PRP8 functions in cis- and trans-splicing
(12).
In this study, we have purified the SL RNP particle from the
trypanosomatid Leptomonas collosoma using a combination of
conventional chromatography and affinity selection with biotinylated
2'-O-methyl (2'-OMe) antisense RNA oligonucleotide,
resulting in the identification of a subset of core proteins and
loosely bound proteins that were selected with the SL RNA. The L. collosoma proteins show immunological relationship to the T. brucei core proteins. Based on internal peptide sequences, one of
the core proteins was cloned and sequenced; the analysis identified it
as a bona fide Sm protein harboring the conserved Sm motifs
1 and 2, mostly related to the SmE protein. In sum, although snRNP
proteins are not recognized by anti-Sm sera in trypanosomes and the Sm
site is degenerate, trypanosomes do possess Sm proteins.
 |
EXPERIMENTAL PROCEDURES |
Extract Preparation and Antisense 2'-OMe RNA Affinity
Purification of SL RNP--
L. collosoma cell culture and
extract preparation (using 0.3 or 0.4 M KCl) has been
previously described (17), as well as post-ribosomal supernatant
preparation and DEAE chromatography (10). Extracts were prepared from
10 liters of cell cultures (5 × 107 cells/ml). The
extract was fractionated on a DEAE-Sephacel column, and the material
eluted at 0.4 M KCl was concentrated to 0.5-1 ml by
chromatography on a 0.2-ml DEAE column. Affinity selection was
performed (11), using oligonucleotide SL-1
(5'-GGAAGUCUCUACAUACXXXXA-3'), complementary to nucleotides 43-57 of
the L. collosoma SL RNA. All nucleotides in the SL-1 are
2'-O-methylated except X, which is biotinylated
2'-deoxythymidine. For U2 snRNP selections, U2-1 oligonucleotide
5'-UXXXXUAGCCGAGAAGAUAU-3', complementary to nucleotides 1-15 of
T. brucei U2 RNA, was used (11). The concentrated RNP fraction (1 ml) was used for selection as described previously (11).
Proteins were eluted in the presence of urea, precipitated with
acetone, and analyzed on a 12% Tris-Tricine gel (18). The selected
proteins were sliced from the gel, digested with LysC, and subjected to
automatic protein sequencing (Technion, Institute of Technology, Haifa,
Israel). RNA was released from the streptavidin-agarose beads as
described previously (11) and was analyzed on a 6% denaturing gel. As
a control, the selection was performed in the absence of oligonucleotide.
Primers--
The primers used were: 1) 9825, 5'-GCCCGAAAGCTCGGTC-3', complementary to nucleotides 80-95 of the
L. collosoma SL RNA; 2) 24279, 5'-TTCATRAATCRTCXTANCC-3'
antisense to the Sm1 peptide IEGNLLGYDEFMNVVL; 3) 24280, 5'-GGNTAXGAYGAX-TTYATGAA-3', sense to Sm1 motif; and 4) 24281, 5'-ACNACXCCNACXTTRTC-3', antisense to Sm2 peptide sequence
ILLRSXDNVGVVVAI. X denotes inosine, N is a mixture of all four
nucleotides, R denotes purines, and Y denotes pyrimidines.
Cloning and Sequencing--
500 ng of degenerate
oligonucleotides 24279, 24280, and 24281 were labeled each with 250 µCi of [
-32P]ATP (7000 Ci/mmol) and polynucleotide
kinase. Each labeled oligonucleotide (108 Cerenkov counts)
was used to screen a
genomic library (50,000 plaques) of L. collosoma (17, 19). Two plaques gave positive signals with all
three probes. Pure
DNA was digested with HpaII and
AluI, and DNA fragments of 0.6 and 1.6 kilobases were cloned into pBluescript SK and sequenced, using T3 and T7 primers.
Native Gels--
RNPs from the different purification steps were
separated on a 5% nondenaturing gel buffered with 50 mM
Tris-glycine, pH 8.8.
 |
RESULTS AND DISCUSSION |
Purification of the L. collosoma SL RNP Core
Particle--
Previously, using affinity selection with biotinylated
RNA oligonucleotide, the SL RNP of T. brucei was purified
and a subset of five low molecular mass proteins of 15 to 8.5 kDa was
identified. Only a single protein of 14.4 kDa appeared to be specific
to SL RNP, whereas other proteins are shared with U2 and U4/U6 RNPs (11). Because of the experimental advantage of performing biochemical analysis with the monogenetic trypanosomatids, we have set up the
purification of the SL RNP from L. collosoma extracts.
Purification steps were scaled-up such that microgram amounts of
proteins sufficient for microsequencing could be prepared. SL RNP was
purified from high-salt extract because only under these conditions was
it possible to recover about 80% of the particles. The SL RNP was
highly enriched by two purification steps: depletion of the ribosomes
and fractionation on a DEAE-Sephacel column. RNA was extracted from the
different purification steps. Results presented in Fig.
1A, lanes 1-3,
demonstrate that this fractionation procedure efficiently enriches for
the major snRNAs, U2, U4, SL, and U6, but that other small RNAs such as
7SL RNA and tRNAs were still present in these fractions. To investigate
the status of the SL RNP during purification, we analyzed the RNPs by
native gel electrophoresis and Northern hybridization. The results
presented in Fig. 1B indicate that in the initial steps of
purification, the SL RNP migrated as a slow form (lane 2)
and was converted to a fast migrating form during fractionation on a
DEAE column (lane 3). Fractionation of the DEAE eluate by CsCl gradient centrifugation suggests that these particles withstand fractionation in high salt gradients and band at a density of ~1.4
g/ml, characteristic of core SL RNP particles (10, 20) (data not
shown). It is currently unknown whether, during the conversion from the
slowly to the fast migrating form of the SL RNP, only particle-specific
proteins are dislodged or whether the SL RNP dissociates from a
multi-snRNP complex. We have previously demonstrated that, when RNPs
extracted at low ionic strength are fractionated on sucrose gradients,
at least 50% of the SL RNP migrates at S values higher than 11 S (core
SL RNP), suggesting that the SL RNP associates with other spliceosomal
components (6). Affinity selection of the SL RNP and U2 RNP from the
DEAE eluate demonstrates its high specificity and efficiency because, in both selections, a single RNA band of the expected size was observed
(Fig. 1A, lanes 4 and 5).

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Fig. 1.
A, RNA analysis of the SL RNP
purification steps. Extracts were prepared from 5 × 1010 cells and fractionated on a DEAE-Sephacel column. The
RNA extracted from the following fractions (0.02 of each sample) was
analyzed on a 6% denaturing gel and visualized by silver stain.
Lane 1, whole cell extract; lane 2,
post-ribosomal supernatant; lane 3, DEAE fraction eluted
with 0.4 M KCl; lane 4, affinity selected
fraction using U2-1 oligonucleotide; and lane 5, affinity
selected fraction using SL-1 oligonucleotide. B, separation
of particles from different purification steps on a native gel. Samples
obtained as described in panel A (0.01 of each) were
fractionated on a 5% native gel. The gel was subjected to Northern
analysis with an anti-SL RNA probe (oligonucleotide 9825). Lane
1, total L. collosoma RNA (10 µg); lane 2,
PRS; and lane 3, DEAE fraction eluted at 0.4 M
KCl.
|
|
Identification of the SL RNP Proteins from L. collosoma--
To
analyze the protein composition of the SL RNP, a concentrated DEAE
column fraction prepared from 1011 cells was used in
affinity selection with biotinylated antisense SL-1 RNA
oligonucleotide. Proteins were analyzed on a 12% Tris-Tricine gel and
stained with Coomassie Blue. Results presented in Fig. 2A show the enrichment of five
proteins of 70, 15, 13, 12, and 8 kDa (lanes 1,
2, 3, and 4). The proteins of ~55
kDa are the most abundant proteins in the DEAE fraction (lanes
4 and 5) and most likely represent
and
tubulins. These proteins were nonspecifically selected because they
were present in the control selection without the SL oligonucleotide
(lane 5). The pattern of the selected small proteins of the
L. collosoma SL RNP seems to differ only slightly from the
pattern of the proteins selected in T. brucei. In addition, the L. collosoma SL RNP contains a protein of 70 kDa.
Because this SL RNP purification was done at 0.4 M KCl, we
will refer to this RNP as the core SL RNP.

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Fig. 2.
A, protein analysis of affinity selected
L. collosoma SL RNP. After selection of SL RNPs from
1011 cells with SL-1 RNA oligonucleotide, proteins were
released, separated on 12% Tris-Tricine gels, and stained with
Coomassie Blue. Markers were low molecular mass markers from Life
Technologies, Inc., and their sizes are indicated on the
right. Extract preparation and affinity selection were
performed in the presence of 0.4 M KCl. Lane 1,
whole cell extract; lane 2, post-ribosomal supernatant;
lane 3, DEAE elution with 0.4 M KCl; lane
4, affinity selection with SL-1 oligonucleotide; and lane
5, control selection in the absence of SL-1 oligonucleotide.
B, the same as in panel A, but extraction was
performed at 0.2 M KCl. Designation of the lanes is as in
panel A.
|
|
To investigate whether purification under less stringent conditions
reveals additional SL RNP associated proteins, particles were extracted
at 0.2 M KCl and were purified by DEAE chromatography. The
selected proteins were stained with Coomassie Blue (Fig.
2B). The results indicate the presence of proteins of 28, 20, and 18 kDa in addition to the four low molecular mass proteins
characteristic of the core SL RNP. However, the 18-kDa protein was
bound nonspecifically to the beads as this protein was present also in
the control selection in the absence of oligonucleotide (Fig.
2B, lane 5). The 70-kDa protein enriched in the
core SL RNP (Fig. 2A, lane 4), was not clearly
seen under low salt conditions (Fig. 2B, lane 4),
most probably because of the nonspecific staining at the upper part of
the gel. The results presented in Fig. 2 demonstrate the specificity of
selection under high salt conditions but also the disadvantage of
loosing additional, weakly associated proteins.
Immunological Relationship of L. collosoma and T. brucei snRNP Core
Proteins--
To examine the relatedness of the core proteins, we used
the antibodies raised against the T. brucei core proteins
(anti-CP) in immunoprecipitation and immunoblotting experiments with
L. collosoma DEAE fraction. The results presented in Fig.
3A demonstrate that anti-CP
antibodies specifically immunoprecipitated the SL RNP because only very
faint background levels of the SL RNA were observed when the nonimmune
serum was used in the experiment (compare lanes 1 and
2). To identify which of the L. collosoma SL RNP
proteins are related to the T. brucei proteins,
affinity-selected L. collosoma proteins were
immunoblotted and reacted with anti-CP antiserum alongside to T. brucei affinity-selected proteins from SL and U2 RNPs. The result
indicates strong reactivity with the 12-kDa protein. The anti-CP
antibodies show the strongest reactivity with the T. brucei
14- and 12.5-kDa proteins (21) migrating close to the immunoreactive
proteins of the L. collosoma SL RNP (Fig. 3B,
lanes 2 and 3). In a control experiment with
nonimmune serum, no reactivity was observed with the L. collosoma proteins (data not shown). The reactivity with the
12-kDa protein indicates that the snRNP core proteins from L. collosoma and T. brucei are immunologically
related.

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Fig. 3.
Immunoprecipitation analysis of L. collosoma SL RNP. A, 50-µl DEAE fraction
obtained from 5 × 109 cells was immunoprecipitated
with 40 µl of anti-CP antibodies (21). RNA was deproteinized and
analyzed by primer extension with anti-SL oligonucleotide 9825, and the
products were separated on a 6% denaturing gel. Lane 1,
pellet obtained with anti-CP antibodies; lane 2, pellet with
nonimmune serum, and lane 3, supernatant of anti-CP
precipitation. The marker was 32P-labeled pBR322
HpaII digest. B, immunoblot analysis of affinity
selected proteins. SL RNP of L. collosoma and SL and U2 RNPs
of T. brucei were affinity purified from a DEAE fraction (as
described above and in Ref. 21), separated by SDS-polyacrylamide gel
electrophoresis, and probed with rabbit anti-CP antibodies as described
previously (11). Immunocomplexes were visualized with goat anti-rabbit
IgG conjugated to horseradish peroxidase and a fluorescent substrate
(ECL). Molecular mass markers are indicated. Lane 1,
L. collosoma SL RNP; lane 2, T. brucei
U2 RNP; and lane 3, T. brucei SL RNP.
|
|
The 12-kDa Protein Is an Sm Protein Homologous to SmE--
To
clone the genes coding for core SL RNP proteins, the low molecular mass
proteins were eluted from the gel and digested with LysC protease.
Several internal peptide sequences were obtained from the four core
proteins. In particular, two long peptides (peptide 1, IEGNLLGYDEFMNVVL; and peptide 2, ILLRSDNVGVVHAI) could be determined
from the 12-kDa protein. Using degenerate oligonucleotides as probes, a
genomic fragment of 1220 base pairs was cloned and sequenced (Fig.
4). An open reading frame was identified
coding for a 11.9-kDa protein of 94 amino acids. The spliced leader
addition site (AG 3' splice site) was mapped 16 nucleotides upstream of the first ATG (data not shown), and 22 consecutive pyrimidines were
found upstream (Fig. 4, underlined in the sequence). These pyrimidines resemble the polypyrimidine tract found in intergenic regions of trypanosomatid genes that was shown to be essential for
accurate trans-splicing (22). The polyadenylation site was mapped by reverse transcriptase polymerase chain reaction and is
located 417 nucleotides downstream of the stop codon (results not
shown). Southern analysis indicated that the gene is present in a
single copy in the L. collosoma genome (data not shown). A
multiple alignment of the L. collosoma protein with its
homologues is presented in Fig. 5. The
L. collosoma protein is 27% identical and 64% similar to
the human SmE protein. Interestingly, the protein possesses the
bipartite Sm motif that carries two conserved domains Sm1 and Sm2
underlined in Fig. 5 (boundaries according to the nomenclature of Hermann et al. (13): Sm motif 1, 32 amino
acids; Sm motif 2, 14 amino acids). The Sm motifs are the most
conserved domains in SmE protein (~45% identity). Among the few
deviations in the Sm motifs of the L. collosoma protein from
its homologues is position 7 of the Sm2 motif (Arg instead of Lys in
most of the other species). This is especially interesting because Arg is conserved in all Sm2 motifs, but in all E proteins this Arg was
changed to Lys, except for the L. collosoma protein where the canonical Arg is kept. Recently, functional analysis was performed on the yeast SmE protein (23, 24). The results pointed out the
importance of certain hydrophobic residues for cell viability; these
positions are essential for interactions of the protein with SmF and
SmG (24). Interestingly, of these seven important residues, all but one
are either similar or identical in L. collosoma, suggesting that their function may be conserved in the trypanosome protein.

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Fig. 4.
Nucleotide sequence of the putative SmE
homologue from L. collosoma. Nucleotide and amino
acid sequences are numbered separately. Peptides determined by
microsequencing are boxed. The putative polypyrimidine track
is underlined, the spliced leader acceptor site (3' splice
site) is indicated with an arrowhead, and the
polyadenylation site is marked with a point.
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Fig. 5.
Alignment of the SmE homologues. The
alignment was performed using the ClustalW Multiple Sequence Alignment
program and is illustrated using the program SeqVu 1.10. Identity is
represented by gray background, and similarity is
boxed. Abbreviations used are: H. sap.,
Homo sapiens; G. gal., Gallus gallus
(chicken); M. Mus., Mus musculus;
Arabi., Arabidopsis thaliana; O.sat.,
Oryza sativa (rice); S. cer., Saccharomyces
cerevisiae; C. eleg, Caenorhabditis elegans;
L.c., Leptomonas collosoma. The sequences were
obtained from the following references or data base accession numbers:
human, (27); G. gallus, GenBankTM X65702; Mouse
(28); A. thaliana, EST, GenBankTM Z29055;
O. sativa, EST, GenBankTM D23404; C. elegans, GenBankTM Z81071; S. cerevisiae,
(22); L.c., GenBankTM AF126283. The
Sm motifs 1 and 2 are underlined, and the consensus
sequences are given (13).
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|
One of the most intriguing questions regarding the trypanosome core
proteins is the lack of recognition by anti-Sm sera. This finding is
even more surprising after revealing the presence of Sm motifs in the
L. collosoma protein. It was previously suggested that
important domains for Sm autoimmunization are the conserved Sm motifs
(13). This current study suggests that not only are the Sm motifs
involved in B-cells epitope recognition. Alternatively, the trypanosome
Sm motifs may differ from the canonical motifs in those positions that
are essential for recognition by the anti-Sm sera. The number of the
core proteins described in this study is smaller than that observed in
T. brucei (11). Either the L. collosoma SL RNP
composition is less complex than that of T. brucei, or more
than a single polypeptide migrates at the same position of the protein
gel. The latter possibility is more likely, based on the differential
staining intensity of the protein bands (Fig. 2, A and
B). Cloning of the entire subset of the L. collosoma Sm proteins should clarify this issue.
Core proteins assembled on the Sm site of snRNAs were shown to serve as
the recognition signal for the m3G cap methyltransferase (25). Similarly, it was shown that accurate modification of the SL RNA
cap structure in vitro requires the SL RNA to be assembled in a core particle (26). The degeneracy of the Sm site in trypanosomes may reflect that each U snRNA, including the SL RNA, binds different subsets of core proteins. Indeed, the presence of unique proteins in
the low molecular mass range has been observed for the SL and U4/U6
snRNPs (11). This suggests that the different combinations of Sm
proteins determined by the different Sm sites and surrounding sequences
may influence the binding of the different methyltransferases and hence
dictate the particular type of cap modification on the trypanosome snRNA.
 |
ACKNOWLEDGEMENTS |
We thank Ora Asher for excellent technical
assistance and Dr. Christian Tschudi for advice in library screening
with degenerate oligonucleotides.
 |
FOOTNOTES |
*
This work was supported by the German-Israeli Foundation.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
§
To whom correspondence should be addressed. Tel.: 972-8-9343626;
Fax: 972-8-9468256.
 |
ABBREVIATIONS |
The abbreviations used are:
SL, spliced leader;
RNP, ribonucleoprotein;
U snRNA and -RNP, uridylic acid-rich small
nuclear RNA and RNP, respectively;
CP, core proteins;
2'-OMe, 2'-O-methyl;
Tricine, N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine.
 |
REFERENCES |
-
Agabian, N.
(1990)
Cell
61,
1157-1160[Medline]
[Order article via Infotrieve]
-
Ullu, E.,
Günzl, A.,
and Tschudi, C.
(1995)
Molecular Biology of Parasitic Protozoa, pp. 115-133, Tokyo Oxford University Press, Oxford, NY
-
Mottram, J.,
Perry, K. L.,
Lizardi, P. M.,
Lührmann, R.,
Agabian, N.,
and Nelson, R. G.
(1989)
Mol. Cell. Biol.
9,
1212-1223[Medline]
[Order article via Infotrieve]
-
Tschudi, C.,
and Ullu, E.
(1990)
Cell
61,
459-466[Medline]
[Order article via Infotrieve]
-
Dungan, J. D.,
Watkins, K. P.,
and Agabian, N.
(1996)
EMBO J.
15,
4016-4029[Abstract]
-
Xu, Y.-X.,
Ben-Shlomo, H.,
and Michaeli, S.
(1997)
Proc. Natl. Acad. Sci. U. S. A.
94,
8473-8478[Abstract/Free Full Text]
-
Tschudi, C.,
Richards, F. F.,
and Ullu, E.
(1986)
Nucleic Acids Res.
14,
8893-8903[Abstract]
-
Branlant, C.,
Krol, A.,
Ebel, J.,
Lazar, E.,
Haendler, B.,
Jacob, M.,
Sri-Widada, J.,
and Jeanteur, P.
(1980)
EMBO J.
1,
1259-1263
-
Lerner, E. A.,
Lerner, M. R.,
Janeway, C. A. J.,
and Steitz, J. A.
(1981)
Proc. Natl. Acad. Sci. U. S. A.
78,
2737-2741[Abstract]
-
Michaeli, S.,
Roberts, T. G.,
Watkins, K. P.,
and Agabian, N.
(1990)
J. Biol. Chem.
265,
10582-10588[Abstract/Free Full Text]
-
Palfi, Z.,
Günzl, A.,
Cross, M.,
and Bindereif, A.
(1991)
Proc. Natl. Acad. Sci. U. S. A.
88,
9097-9101[Abstract]
-
Lücke, S.,
Klöckner, T.,
Palfi, Z.,
Boshart, M.,
and Bindereif, A.
(1997)
EMBO J.
16,
4433-4440[Abstract/Free Full Text]
-
Hermann, H.,
Fabrizio, P.,
Raker, V. A.,
Foulaki, K.,
Hornig, H.,
Brahms, H.,
and Lührmann, R.
(1995)
EMBO J.
14,
2076-2088[Abstract]
-
Séraphin, B.
(1995)
EMBO J.
14,
2089-2098[Abstract]
-
Cooper, M.,
Johnston, L. H.,
and Beggs, J. D.
(1995)
EMBO J.
14,
2066-2075[Abstract]
-
Cross, M.,
Wieland, B.,
Palfi, Z.,
Günzl, A.,
Röthlisberger, U.,
Lahm, H.-W.,
and Bindereif, A.
(1993)
EMBO J.
12,
1239-1248[Abstract]
-
Goldring, A.,
Karchi, M.,
and Michaeli, S.
(1995)
Exp. Parasitol.
80,
333-338[CrossRef][Medline]
[Order article via Infotrieve]
-
Judd, R. C.
(1994)
in
Methods in Molecular Biology (Walker, J. M., ed), pp. 49-58, Humana Press Inc., Totowa, NJ
-
Goldring, A.,
and Michaeli, S.
(1995)
Gene
156,
139-144[CrossRef][Medline]
[Order article via Infotrieve]
-
Cross, M.,
Günzl, A.,
Palfi, Z.,
and Bindereif, A.
(1991)
Mol. Cell. Biol.
11,
5516-5526[Medline]
[Order article via Infotrieve]
-
Palfi, Z.,
and Bindereif, A.
(1992)
J. Biol. Chem.
267,
20159-20163[Abstract/Free Full Text]
-
Matthews, K. R.,
Tschudi, C.,
and Ullu, E.
(1994)
Genes Dev.
8,
491-501[Abstract]
-
Bordonné, R.,
and Tarassov, I.
(1996)
Gene (Amst.)
176,
111-117[CrossRef][Medline]
[Order article via Infotrieve]
-
Camasses, A.,
Bragado-Nilsson, E.,
Martin, R.,
Séraphin, B.,
and Bordonné, R.
(1998)
Mol. Cell. Biol.
18,
1956-1966[Abstract/Free Full Text]
-
Mattaj, I. W.
(1986)
Cell
46,
905-911[Medline]
[Order article via Infotrieve]
-
Ullu, E.,
and Tschudi, C.
(1995)
J. Biol. Chem.
270,
20365-20369[Abstract/Free Full Text]
-
Stanford, D. R.,
Kehl, M.,
Perry, C. A.,
Holicky, E. L.,
Harven, S. E.,
Rohleder, A. M.,
Rehder, K., Jr.,
Lührmann, R.,
and Wieben, E. D.
(1988)
Nucleic Acids Res.
16,
10593-10605[Abstract]
-
Fautsch, M. P.,
Thompson, M. A.,
Holicky, E. L.,
Schultz, P. J.,
Hallett, J. B.,
and Wieben, E. D.
(1992)
Genomics
14,
883-890[Medline]
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