The Heterogeneous Nuclear Ribonucleoproteins I and K Interact with a Subset of the Ro Ribonucleoprotein-associated Y RNAs in Vitro and in Vivo

The hY RNAs are a group of four small cytoplasmic RNAs of unknown function that are stably associated with at least two proteins, Ro60 and La, to form Ro ribonucleoprotein complexes. Here we show that the heterogeneous nuclear ribonucleoproteins (hnRNP) I and K are able to associate with a subset of hY RNAs in vitro and demonstrate these interactions to occur also in vivo in a yeast three-hybrid system. Experiments performed in vitro and in vivo with deletion mutants of hY1 RNA revealed its pyrimidine-rich central loop to be involved in interactions with both hnRNP I and K and clearly showed their binding sites to be different from the Ro60 binding site. Both hY1 and hY3 RNAs coprecipitated with hnRNP I in immunoprecipitation experiments performed with HeLa S100 extracts and cell extracts from COS-1 cells transiently transfected with VSV-G-tagged hnRNP-I, respectively. Furthermore, both anti-Ro60 and anti-La antibodies coprecipitated hnRNP I, whereas coprecipitation of hnRNP K was not observed. Taken together, these data strongly suggest that hnRNP I is a stable component of a subpopulation of Ro RNPs, whereas hnRNP K may be transiently bound or interact only with (rare) Y RNAs that are devoid of Ro60 and La. Given that functions related to translation regulation have been assigned to both proteins and also to La, our findings may provide novel clues toward understanding the role of Y RNAs and their respective RNP complexes. The hY RNAs are a group of four small cytoplasmic RNAs of unknown function that are stably associated with at least two proteins, Ro60 and La, to form Ro ribonucleoprotein complexes. Here we show that the heterogeneous nuclear ribonucleoproteins (hnRNP) I and K are able to associate with a subset of hY RNAs in vitro and demonstrate these interactions to occur also in vivo in a yeast three-hybrid system. Experiments performed in vitro and in vivo with deletion mutants of hY1 RNA revealed its pyrimidine-rich central loop to be involved in interactions with both hnRNP I and K and clearly showed their binding sites to be different from the Ro60 binding site. Both hY1 and hY3 RNAs coprecipitated with hnRNP I in immunoprecipitation experiments performed with HeLa S100 extracts and cell extracts from COS-1 cells transiently transfected with VSV-G-tagged hnRNP-I, respectively. Furthermore, both anti-Ro60 and anti-La antibodies coprecipitated hnRNP I, whereas coprecipitation of hnRNP K was not observed. Taken together, these data strongly suggest that hnRNP I is a stable component of a subpopulation of Ro RNPs, whereas hnRNP K may be transiently bound or interact only with (rare) Y RNAs that are devoid of Ro60 and La. Given that functions related to translation regulation have been assigned to both proteins and also to La, our findings may provide novel clues toward understanding the role of Y RNAs and their respective RNP complexes. ribonucleoprotein heterogeneous nuclear ribonucleoprotein immunoprecipitation buffer polypyrimidine tract-binding protein systemic lupus erythematosus vesicular stomatitis virus β-galactosidase polyacrylamide gel electrophoresis dithiothreitol 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid polymerase chain reaction 5-bromo-4-chloro-3-indolyl β-d-galactopyranoside. Small ribonucleoprotein (RNP)1 complexes are usually composed of one molecule of a small RNA and several proteins that bind either directly to the RNA or indirectly via protein-protein interactions (1Varani G. Nagai K. Annu. Rev. Biophys. Biomol. Struct. 1998; 27: 407-445Crossref PubMed Scopus (252) Google Scholar, 2Yu Y.-T. Scharl E.C. Smith C.M. Steitz J.A. Gesteland R.F. Cech T.R. Atkins J.F. The RNA World. Cold Spring Harbor Laboratory, Cold Spring Harbor, NY1999: 487-524Google Scholar). Many of these complexes exert essential functions that are often indispensable for survival, such as the small nuclear RNPs, which are major components of the spliceosomal machinery, or the signal recognition particle, which plays a key role in protein export. In contrast to these well defined complexes, the structure of the cytoplasmic Ro RNPs is still not fully resolved, and their function has remained enigmatic (3Pruijn G.J.M. Simons F.H.M. Van Venrooij W.J. Eur. J. Cell Biol. 1997; 74: 123-132PubMed Google Scholar, 4Labbe J.C. Hekimi S. Rokeach L.A. Biochem. Cell Biol. 1999; 77: 349-354Crossref PubMed Google Scholar). They are composed of one molecule of a small Y RNA (transcribed by RNA polymerase III) and at least two proteins, the 60-kDa protein Ro60 and the 48-kDa phosphoprotein La. However, although Ro60 and Y RNAs are present in comparable stochiometric amounts, La is ∼50-fold more abundant, and therefore the vast majority of La molecules is not bound to Y RNAs, in contrast to Ro60 (5Peek R. Pruijn G.J.M. Van der Kemp A.J.W. Van Venrooij W.J. J. Cell Sci. 1993; 106: 929-935PubMed Google Scholar). Y RNAs are highly conserved in evolution (6Pruijn G.J. Wingens P.A. Peters S.L. Thijssen J.P. van Venrooij W.J. Biochim. Biophys. Acta. 1993; 1216: 395-401Crossref PubMed Scopus (55) Google Scholar) and have been found in all multicellular eukaryotic organisms and may also be present in some bacteria (7Chen X.G. Quinn A.M. Wolin S.L. Genes Dev. 2000; 14: 777-782PubMed Google Scholar) but, remarkably, have so far not been detected in yeast. Interestingly, the genome of the nematode Caenorhabditis elegans contains only one functional Y RNA gene, whereas in humans and other vertebrates four closely related Y RNA species exist. Unlike other RNA polymerase III transcripts, Y RNAs retain the oligo(U) stretch at their 3′ end that forms the binding site for La; therefore these RNAs remain permanently associated with La (5Peek R. Pruijn G.J.M. Van der Kemp A.J.W. Van Venrooij W.J. J. Cell Sci. 1993; 106: 929-935PubMed Google Scholar, 8Boire G. Craft J. J. Clin. Invest. 1990; 85: 1182-1190Crossref PubMed Scopus (102) Google Scholar). On the other hand, nuclear Y RNAs do not seem to be associated with Ro60, and it was suggested that Ro RNPs assemble upon export to the cytoplasm (3Pruijn G.J.M. Simons F.H.M. Van Venrooij W.J. Eur. J. Cell Biol. 1997; 74: 123-132PubMed Google Scholar,9Simons F.H.M. Van Venrooij W.J. Pruijn G.J.M. Google Scholar). functions have been for La, regulation of RNA polymerase III Steitz J.A. J. PubMed Scopus Google Scholar, Sci. S. Scopus Google Scholar, Genes Dev. 1999; PubMed Scopus Google in and translation G.J. Google Scholar, Biol. 2000; PubMed Scopus Google and a role in the of small nuclear RNPs Wolin S.L. J. 2000; PubMed Scopus Google it is still not which role nuclear and cytoplasmic protein plays in In it is unknown a function be to Y La. is of Ro60 J.C. Hekimi S. Rokeach L.A. Biochem. Cell Biol. 1999; 77: 349-354Crossref PubMed Google Scholar). In the cytoplasm it may be involved in the regulation of translation as for protein in J. Biol. 1998; PubMed Scopus Google Scholar) and in the Ro60 may be in a of by and molecules Wolin S.L. Genes Dev. PubMed Scopus Google Scholar, J.C. J. Rokeach L.A. Hekimi S. Sci. S. 2000; PubMed Scopus Google Scholar). However, these functions do not seem to be the of Y RNAs in in Interestingly, a of Ro60 was in the that to to the of to (7Chen X.G. Quinn A.M. Wolin S.L. Genes Dev. 2000; 14: 777-782PubMed Google Scholar). may to a RNA function of Ro60 as has been for La Wolin S.L. J. 1998; PubMed Scopus Google Scholar). the stable of Ro60 and La with Y RNAs is the of other components in to Ro60 and La is still a of the suggested of a protein and the protein have remained J. PubMed Scopus Google Scholar, Van Venrooij W.J. Pruijn G.J.M. J. Biol. PubMed Scopus Google Scholar, J. Clin. Invest. PubMed Google Scholar, G. Clin. PubMed Scopus Google Scholar, J. Google Scholar, J. G. Rev. 1998; PubMed Scopus Google and interactions of two novel proteins with Ro60 in yeast and three-hybrid to be J.P. J. Clin. Invest. 1999; PubMed Scopus Google Scholar, G. 2000; PubMed Scopus Google Scholar). In a we in vitro binding of several proteins in a HeLa S100 to hY RNAs G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). proteins and bound to hY1 and hY3 RNA only or not at all to and Interestingly, to these proteins found in from with the systemic lupus erythematosus to Ro and La J. 1993; PubMed Scopus Google Scholar). deletion mutants of hY1 RNA we able to show that the binding sites for these proteins from the Ro60 binding site. In we demonstrate that two of these proteins are to the heterogeneous nuclear RNP proteins I and K and present that are able to associate with a subset of hY RNAs in of proteins binding to hY1 and hY3 RNA in from a with antibodies to these proteins was G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). from and from with do not or anti-La as antibodies anti-La G.J. Thijssen J.P. Smith Van Venrooij W.J. Eur. J. Biochem. PubMed Scopus Google anti-Ro60 Pruijn G.J. J.F. Thijssen J.P. Van der Kemp Van Venrooij W.J. Clin. PubMed Scopus Google K G. Biol. PubMed Scopus Google of of G.J. R. 1998; PubMed Scopus Google of Cold Spring Harbor and as HeLa S100 extracts for in as G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). HeLa cells Cell in buffer in of buffer and by by at and the was for at and for at the protein the S100 was at immunoprecipitation experiments with transfected COS-1 cell extracts and of the cells with with a for at in buffer cell was by and the was at by and as G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar, G. G. J. Google Scholar). The for with in buffer and for either with or with respectively. the with bound antibodies detected by or from transfected cells by and a the in buffer for at with in buffer for at bound antibodies detected by as with antibodies to Ro60, La, and hnRNP I and K performed as with antibodies to protein as a G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). of a HeLa cell was in of immunoprecipitation buffer and for at with antibodies of with and in of RNA was with with of as and by of proteins of a HeLa cell was to of or anti-La a at a with at least of proteins with with extracts from transfected antibodies or to protein by at in buffer the with and with cell extracts for at the with and RNAs by and In vitro of and hY RNAs and of hY1 RNA deletion mutants was performed as G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). RNAs was at for of RNAs and of The was a of K. for of Y RNAs by RNAs by and with hY RNA by at as G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar, G. G. J. Google Scholar). performed as G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). complexes, the of the HeLa was to by of of hY RNA or RNA and yeast was and the was to by with buffer for at hY RNP complexes by of and for at with of and bound proteins buffer proteins for at and by of and of at for at least and for at proteins either in buffer for or in buffer for in binding to hY RNAs in vitro in of buffer gel electrophoresis was in buffer the a electrophoresis in a at at at and at at The for in buffer of and for in buffer in buffer for a and of a polyacrylamide was for at and the with or for to proteins binding to hY1 RNA not to and to by performed in gel VSV-G-tagged as the La protein the was via the and a La G.J. Van Venrooij W.J. PubMed Scopus Google Scholar) as in are the and The is The was with and the sites of the The hnRNP K and hnRNP I by of The hnRNP K was by to and of the La with the hnRNP K which in VSV-G-tagged hnRNP K in of a hnRNP I in was to the with a The of the was by a the was in cells transiently transfected with the COS-1 cells to in with and in at and in transfected with of in a of of was performed at and a of with a the cells in and the of hnRNP I and hnRNP K with hY RNAs in a three-hybrid S. Sci. S. PubMed Scopus Google Scholar) was The The hY RNAs and hY1 RNA deletion mutants the sites of the RNA of two of the RNA hnRNP I and hnRNP K by the and sites of the protein The and of all was by The yeast which stably the protein was with the RNAs and the proteins, respectively. and of the proteins was by for β-galactosidase a as a and for of cells with of protein was at as a a the was S. Sci. S. PubMed Scopus Google Scholar). we have a of proteins with and that in to Ro60 and La bound to hY to hY1 and hY3 RNA G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). Interestingly, to these proteins detected in several of with antibodies to Ro and La these hY proteins Ro RNP complexes in vitro by HeLa S100 extracts with hY1 performed in to for binding with a of yeast as a complexes by by gel electrophoresis and by to all novel hY proteins as well as Ro60 and La G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google also be in several protein the by The to proteins binding to hY1 RNA are by The of Ro60 and La with its Biol. PubMed Scopus Google Scholar, J. Biochim. Biophys. Acta. PubMed Scopus Google Scholar, G. Van der Van Venrooij W.J. Pruijn G.J.M. 2000; PubMed Scopus Google Scholar) in a and antibodies to these proteins the two the La La from the to Ro60 and La proteins, four major protein be detected The of these proteins, which at was from a gel in with and by a acid which a in the hnRNP K protein was with the of the proteins in our which to the and for hnRNP K S. G. Genes Dev. PubMed Scopus Google of hY1 proteins by gel electrophoresis and from HeLa cell extracts binding to hY1 RNA in by to a and with from a with several hY1 proteins in to Ro60 and La The two La La of Ro60 and La in a antibodies to these The hnRNP K protein was by the of hnRNP I as a was from its the gel and a hnRNP I The protein that we was a protein as a experiments suggested the of a 60-kDa protein in hY1 RNPs that with Ro60 in and to have RNA binding as the protein G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). of its and we that protein was hnRNP I, the which is to as a of in and has a of S. G. Genes Dev. PubMed Scopus Google S. G. PubMed Scopus Google Scholar). the of hnRNP I and hnRNP K in complexes hY1 proteins by and with either or antibodies to hnRNP K or hnRNP I, with our data proteins of and in to Ro60 and La G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). In contrast to the K the whereas the I two of and the the antibodies a protein in the proteins binding to the other hY1 proteins by the the protein was and only with the and therefore not be the protein as a at and for the at with hnRNP K in data be and the protein was not the of hnRNP I and hnRNP K with hY RNAs in more performed with all four hY RNAs as well as with several deletion mutants of hY1 binding to hY RNAs by and with antibodies to hnRNP I and K as both proteins showed binding to hY1 only hnRNP I bound to hY3 whereas the of hnRNP K with hY3 RNA was In of the two proteins with or data G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). the of hY1 RNA involved in binding of the two proteins, deletion mutants of hY1 RNA of the Ro60 binding site not have binding of either hnRNP I or hnRNP K whereas of the La binding site to binding of both proteins The was with a the pyrimidine-rich central loop which bound hnRNP I and hnRNP K not at all of or of or only binding of hnRNP I, whereas binding of hnRNP K to be by and the binding of both proteins to be with a the comparable was with hnRNP I and K proteins in vitro in a not Taken together, these clearly the in vitro binding of hnRNP I and K to hY1 showed the of the two proteins with hY3 RNA to be or with hY1 the central loop to be indispensable for binding of both proteins to hY1 suggested that La not Ro60 is for and that the binding sites for the two hnRNP proteins are closely not and which hY RNAs are associated with the hnRNP I and K proteins in a HeLa cell was to immunoprecipitation antibodies to hnRNP I, hnRNP Ro60, and La. RNAs from the by and with hY RNAs by in coprecipitation of hY1 and hY3 RNA by the I was clearly although at a as with the with the anti-La and anti-Ro60 which all four hY RNA hY1 RNA and hY3 RNA and to of these two hY RNAs as and RNAs J. Clin. Invest. PubMed Google Scholar, S.L. Steitz J.A. PubMed Scopus Google which was with the of coprecipitation of these molecules by the anti-La not only the binding of hnRNP I to hY1 and hY3 RNA in vitro also strongly suggested that hnRNP I is associated with hY1 and hY3 RNA in In coprecipitation of hY RNAs by the K was not these data suggested that the of hnRNP I with hY1 and hY3 RNA also in not to that protein was present also in Ro RNPs RNA complexes both Ro60 and Ro and La RNPs from a HeLa cell anti-Ro60 and anti-La with by and by antibodies hnRNP I and hnRNP proteins from in vitro hY1 RNPs as In these experiments the of hnRNP I in both anti-La and anti-Ro60 was and that protein was in Ro RNP complexes. On the other hand, and in with the RNA hnRNP K not be detected in these these data and to for the that the by the K be the hnRNP K is with hY we both hnRNP proteins as a La as VSV-G-tagged proteins in transiently transfected COS-1 with a to the that the proteins are to was to of transfected cells that for the of Y RNAs by by hnRNP I was found to associate with and RNA and of hnRNP K with Y RNAs be detected VSV-G-tagged La was associated with all four Y RNAs and Y RNAs cells transfected with four Y RNAs also coprecipitated by the anti-La and anti-Ro60 and the interactions of hnRNP I and hnRNP K with hY RNAs in a we of the yeast three-hybrid S. Sci. S. PubMed Scopus Google Scholar). In to the is of the and upon of RNA with the protein of In our the of the of the to the protein the of hY RNA hY1 RNA deletion of the RNA and the was composed of the of to either hnRNP I or hnRNP K the of hY1 and hY3 RNA with hnRNP I or hnRNP a yeast the protein was with the these RNAs and of the or components not able to a of and showed or only a and In was clearly in hY1 RNA and hnRNP I or hnRNP K whereas only by in hY3 RNA The interactions of hY1 RNA with the two hnRNP proteins in the yeast with the in data of hnRNP I with hY3 the other hand, in the in vitro binding we binding of hnRNP I and K to hY1 RNA deletion mutants as in the pyrimidine-rich showed only of with either hnRNP K or hnRNP I, with the in vitro In of the was that of RNA for both hnRNP I and whereas deletion of to a of the with both hnRNP The other two hY1 RNA mutants showed as hY1 data from several suggest that Ro RNP complexes may a of other proteins in to Ro60 and La J. PubMed Scopus Google Scholar, Van Venrooij W.J. Pruijn G.J.M. J. Biol. PubMed Scopus Google Scholar, J. Clin. Invest. PubMed Google Scholar, G. Clin. PubMed Scopus Google Scholar, J. Google Scholar, J. G. Rev. 1998; PubMed Scopus Google Scholar, J.P. J. Clin. Invest. 1999; PubMed Scopus Google Scholar, G. 2000; PubMed Scopus Google Scholar, G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google for has not been (3Pruijn G.J.M. Simons F.H.M. Van Venrooij W.J. Eur. J. Cell Biol. 1997; 74: 123-132PubMed Google Scholar, 4Labbe J.C. Hekimi S. Rokeach L.A. Biochem. Cell Biol. 1999; 77: 349-354Crossref PubMed Google Scholar). Here we have two of the proteins by to associate with hY RNAs in vitro G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar) as hnRNP I and hnRNP K. The two proteins strongly with hY1 RNA and to a with hY3 RNA not with or which is in with our experiments performed with extracts from HeLa cells and transiently transfected COS-1 cells for in vivo of hnRNP I with hY1 and hY3 RNA and the of a subpopulation of Ro RNPs hnRNP I in to Ro60 and La. The that the I of hY RNAs the anti-Ro60 comparable of Ro60 and hnRNP I to be bound in the in contrast to Ro60, hnRNP I is associated with a of hY1 and hY3 these not provide for hY K interactions in these a clearly was in a yeast three-hybrid that was comparable with that with hnRNP hnRNP K may bind only to a subset of hY RNAs that are devoid of Ro60 is Ro60 in and therefore to the with hY RNAs may have been of the extracts or upon binding in immunoprecipitation The of La binding site for binding of hnRNP I and hnRNP K was and to that the function of La in hY RNP may be that of RNA for of hY RNAs, binding of other proteins the of be with the role of La in small nuclear RNP and Genes Dev. 1999; PubMed Scopus Google Scholar, Wolin S.L. J. 2000; PubMed Scopus Google Scholar, Wolin S.L. J. 1998; PubMed Scopus Google Scholar). 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PubMed Google Scholar, G. Clin. PubMed Scopus Google Scholar, G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). The of Y RNAs has the evolution from which only one Y to vertebrates with four Y RNAs (6Pruijn G.J. Wingens P.A. Peters S.L. Thijssen J.P. van Venrooij W.J. Biochim. Biophys. Acta. 1993; 1216: 395-401Crossref PubMed Scopus (55) Google Scholar, Van Venrooij W.J. Pruijn G.J. 2000; PubMed Scopus Google Scholar). Interestingly, the Ro60 binding site and the pyrimidine-rich loop the conserved present in elegans which the to hY3 RNA PubMed Scopus Google Scholar). strongly that the pyrimidine-rich is for Y RNA interactions with other proteins Furthermore, the loop of hY1 RNA was to be to and Thijssen J.P. E.C. Van Venrooij W.J. Pruijn G.J. PubMed Scopus Google also with pyrimidine-rich of other small RNAs by RNA polymerase III J. Biol. 1990; PubMed Google Scholar, J. 1993; PubMed Google Scholar, Biol. 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J. 1997; PubMed Scopus Google Scholar, 1997; PubMed Scopus Google Scholar, J. Biol. 2000; PubMed Scopus Google Scholar). Given that Ro RNPs are not in the it is to functions of hnRNP I and K that are related to hnRNP I has been to bind to several binding in a Sci. S. 1993; PubMed Scopus Google Scholar, R. J. Biol. 2000; PubMed Scopus Google Scholar, R. R. Biol. 2000; PubMed Scopus Google Scholar). a was also found for La G.J. Google and of these two proteins in the regulation of translation has been suggested J. 1999; PubMed Scopus Google Scholar). Furthermore, these proteins may be also for and of translation by translation of G. J. PubMed Scopus Google Scholar). from its role as K. Van J. 1997; PubMed Scopus Google Scholar, S. J. Biol. PubMed Scopus Google Scholar, Biol. PubMed Scopus Google hnRNP K protein has been to as a by of its binding to the at the 3′ end of the translation 1997; PubMed Scopus Google Scholar). In a translation of virus is by hnRNP K and the protein S. J. Biol. 1998; PubMed Scopus Google Scholar). Furthermore, two functions have been assigned to the Ro60 in a for Wolin S.L. Genes Dev. PubMed Scopus Google Scholar) and a role in the regulation of translation of protein in with La and protein by binding to a polypyrimidine stretch in the of J. Biol. 1998; PubMed Scopus Google Scholar, J. Biol. PubMed Scopus Google Scholar). our data and of one may the role of Ro RNPs or hY RNPs, hY RNAs associate with La and the toward the nuclear Ro60 to export the indispensable for nuclear export of hY RNAs (3Pruijn G.J.M. Simons F.H.M. Van Venrooij W.J. Eur. J. Cell Biol. 1997; 74: 123-132PubMed Google Scholar, F.H.M. Van Venrooij W.J. Pruijn G.J.M. Google Scholar). their of hY RNPs are by of with proteins hnRNP I and and other proteins to interact with hY RNA in vitro or with Ro60 in yeast and three-hybrid J.P. J. Clin. Invest. 1999; PubMed Scopus Google Scholar, G. 2000; PubMed Scopus Google Scholar, G. Pruijn G.J.M. G. Eur. J. Biochem. 2000; PubMed Scopus Google Scholar). these proteins may be and upon binding to hY RNAs to exert functions either in the in the or in the is that for all four hY proteins to Ro60, and hnRNP I and in translation of and have been although these proteins as nuclear proteins with functions related to RNA and hY RNAs may as for proteins involved in regulation of Taken together, we that our findings not only of the structure of Ro RNP hY complexes also may provide some clues their which be in G. for for hnRNP I and K and for the for for and van Venrooij for and for and The of for to the for protein in