CHICKEN YB-2, A Y-BOX PROTEIN, IS A POTENT ACTIVATOR OF ROUS-SARCOMA VIRUS LONG TERMINAL REPEAT-DRIVEN TRANSCRIPTION IN AVIAN FIBROBLASTS

We have previously reported on the cloning and characterization of chk -YB-2, a novel member of the Y-box family of proteins, that binds to t he sequence 5'-GTACCACC-3' present on the noncoding strand of the Rous sarcoma virus (RSV) long terminal repeat (LTR) in a single-strand-spe cific manner. Here, we demonstrate that deletion or mutation of this m otif not only eliminates chk-YB-2 binding in vitro but also down-regul ates RSV LTR-driven transcription in avian cells. Selective abrogation of chk-YB-2, expression by using antisense oligonucleotides decreased RSV LTR-driven transcription in a promoter-specific manner. This inhi bition was not observed when a reporter construct with a deletion in t he chk-YB-2 binding site was used, Depletion of cellular chk-YB-2 by t ransfecting the cells with excess of its recognition sequence oligonuc leotides also resulted in reduced transcription from the RSV LTR, Take n together, these results suggest that chk-YB-2 acts as an activator o f LTR-promoted transcription in avian cells and that this activation i s mediated primarily through the sequence 5'-GTACCACC-3'.