RNA chaperone activity of protein components of human Ro RNPs.
Ro ribonucleoprotein (RNP) complexes are composed of one molecule of a small noncoding cytoplasmic RNA, termed Y RNA, and the two proteins Ro60 and La. Additional proteins such as hnRNP I, hnRNP K, or nucleolin have recently been shown to be associated with subpopulations of Y RNAs. Ro RNPs appear to be localized in the cytoplasm of all higher eukaryotic cells but their functions have remained elusive. To shed light on possible functions of Ro RNPs, we tested protein components of these complexes for RNA chaperone properties employing two in vitro chaperone assays and additionally an in vivo chaperone assay. In these assays the splicing activity of a group I intron is measured. La showed pronounced RNA chaperone activity in the cis-splicing assay in vitro and also in vivo, whereas no activity was seen in the trans-splicing assay in vitro. Both hnRNP I and hnRNP K exhibited strong chaperone activity in the two in vitro assays, however, proved to be cytotoxic in the in vivo assay. No chaperone activity was observed for Ro60 in vitro and a moderate activity was detected in vivo. In vitro chaperone activities of La and hnRNP I were completely inhibited upon binding of Y RNA. Taken together, these data suggest that the Ro RNP components La, hnRNP K, and hnRNP I possess RNA chaperone activity, while Ro60-Y RNA complexes might function as transporters, bringing other Y RNA binding proteins to their specific targets.
Belisova
Aurélia
A
Department of Medical Biochemistry, Medical University of Vienna, Vienna Biocenter, Dr. Bohrgasse 9, A-1030 Vienna, Austria.
Semrad
Katharina
K
Mayer
Oliver
O
Kocian
Grazia
G
Waigmann
Elisabeth
E
Schroeder
Renée
R
Steiner
Günter
G
D001324:Autoantigens / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007438:Introns; D018832:Molecular Chaperones / Q000378:metabolism*; D009154:Mutation; D011485:Protein Binding; D012313:RNA / Q000378:metabolism*; D020733:RNA, Small Cytoplasmic / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D012261:Ribonucleoproteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D013462:Sulfur Radioisotopes / Q000378:metabolism; D020040:Trans-Splicing; D014158:Transcription, Genetic; D000097585:SS-B Antigen; D000099207:SS-A Antigen
D001324:Autoantigens; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D018832:Molecular Chaperones; D012313:RNA; D020733:RNA, Small Cytoplasmic; D011994:Recombinant Proteins; D012261:Ribonucleoproteins; D013462:Sulfur Radioisotopes; D000097585:SS-B Antigen; D000099207:SS-A Antigen; C116006:RO60 protein, human