Chicken Y-box proteins chk-YB-1b and chk-YB-2 repress translation by sequence-specific interaction with single-stranded RNA

Y-Box proteins comprise a large family of multifunctional proteins with a w ide spectrum of activities in both transcription and translational regulati on of gene expression. Earlier, we have reported on the involvement of chk- YB-2 in transcriptional regulation of Rous sarcoma virus long terminal repe ats and the involvement of chk-YB-1b in transcriptional regulation of alpha 1(I) collagen genes. Here, we have investigated the potential role of chk- YB-2 and chk-YB-1b in RNA metabolism. We report that chk-YB-2 and chk-YB-1b are localized predominantly in the cytoplasm and that they both can bind s ingle-stranded RNA in a sequence-specific and reversible manner. Well-conse rved cold-shock domain, N-terminal proline-rich domain and the alternating clusters of acidic and basic amino acids located in the C-terminal ends of these two proteins were all found to be necessary for their RNA-binding abi lity. Further, we demonstrate that these two proteins inhibit translation i n vitro and that binding to RNA is required for this inhibition, The signif icance of these results is discussed.