Open AccessS1 proteins C2 and D2 are novel hnRNPs similar to the transcriptional repressor, CArG box motif‐binding factor A
Author(s) -
Inoue Akira,
Omori Akira,
Ichinose Sachiyo,
Takahashi Kenichi P.,
Kinoshita Yosihiro,
Mita Shiro
Publication year - 2001
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.2001.02267.x
Subject(s) - nuclear protein , heterogeneous nuclear ribonucleoprotein , microbiology and biotechnology , biology , heterogeneous ribonucleoprotein particle , rnase p , immunoprecipitation , ribonucleoprotein , repressor , binding protein , transcription factor , gene , rna binding protein , messenger rna , biochemistry , rna
S1 proteins A–D are liberated from thoroughly washed nuclei by mild digestion with DNase I or RNase A, and extracted selectively at pH 4.9 from the reaction supernatants. Here, we characterized the S1 proteins, focusing on protein D2, the most abundant S1 protein in the rat liver, and on protein C2 as well. Using a specific antibody, McAb 351, they were shown to occur in the extranucleolar nucleoplasm, and to be extracted partly in the nuclear soluble fraction. We demonstrate that the S1 proteins in this fraction exist constituting heterogeneous nuclear ribonucleoproteins (hnRNPs), through direct binding to hnRNAs, as revealed by centrifugation on density gradients, immunoprecipitation, and UV cross‐linking. In hnRNPs, protein D2 occurred at nuclease‐hypersensitive sites and C2 in the structures that gave rise to 40 S RNP particles. By microsequencing, protein D2 was identified with a known protein, CArG box motif‐binding factor A (CBF‐A), which has been characterized as a transcriptional repressor, and C2 as its isoform protein. In fact, CBF‐A expressed from its cDNA was indistinguishable from protein D2 in molecular size and immunoreactivity to McAb 351. Thus, the present results demonstrate that S1 proteins C2 and D2 are novel hnRNP proteins, and suggest that the proteins C2 and D2 act in both transcriptional and post‐transcriptional processes in gene expression.