HERPESVIRUS SAIMIRI SMALL RNA AND INTERLEUKIN-4 MESSENGER-RNA AUUUA REPEATS COMPETE FOR SEQUENCE-SPECIFIC FACTORS INCLUDING A NOVEL 70K PROTEIN

A highly oncogenic strain of the lymphotropic tumour virus herpesvirus saimiri (HVS; strain 484-77) expresses four small RNAs (HSUR1 to 4) i n high copy numbers in transformed T cells. In HSUR1 and HSUR2 the 5' terminal regions contain conserved AUUUA sequence repeats. The same AU UUA repeats occur in the 3' non-coding regions of growth factor, lymph okine and protooncogene mRNAs, and the sequence is involved in rapid m RNA degradation. We report here that by using a highly specific u.v. c ross-linking method we identified a novel 70K binding factor with AUUU A sequence specificity. Non-radiolabelled competition and V8 protease analysis show that the protein can form a complex with the 3' non-codi ng region of interleukin-4 mRNA and bind the AUUUA repeats of a HVS sm all RNA. We also detected an AUUUA-specific minor 32K human protein wi th the same electrophoretic mobility as a marmoset factor implicated i n growth factor mRNA destabilization. The findings are consistent with the hypothesis that the viral small RNAs can compete for factors invo lved in rapid degradation of growth factor mRNAs and may contribute to viral oncogenesis.