Characterization of the 5'-untranslated region of YB-1 mRNA and autoregulation of translation by YB-1 protein.

The eukaryotic Y-box binding protein YB-1 is involved in various biological processes, including DNA repair, cell proliferation and the regulation of transcription and translation. YB-1 protein is abundant and expressed ubiquitously in human cells, functioning in cell proliferation and transformation. Its concentration is thought to be highly regulated at both the levels of transcription and translation. Therefore, we investigated whether or not the 5'-UTR of YB-1 mRNA affects the translation of YB-1 protein, thus influencing expression levels. Luciferase mRNA ligated to the YB-1 mRNA 5'-UTR was used as a reporter construct. Ligation of the full-length YB-1 5'-UTR (331 bases) enhanced translation as assessed by in vitro and in vivo translation assays. Deletion constructs of the YB-1 5'-UTR also resulted in a higher efficiency of translation, especially in the region mapped to +197 to +331 from the major transcription start site. RNA gel shift assays revealed that the affinity of YB-1 for various 5'-UTR probe sequences was higher for the full-length 5'-UTR than for deleted 5'-UTR sequences. An in vitro translation assay was used to demonstrate that recombinant YB-1 protein inhibited translation of the full-length 5'-UTR of YB-1 mRNA. Thus, our findings provide evidence for the autoregulation of YB-1 mRNA translation via the 5'-UTR.