Adeno-associated virus type 2 nonstructural protein Rep78 suppresses translation in vitro

Adeno-associated virus type 2 nonstructural protein Rep78 [621 amino acids (aa) long] affects the expression of various cellular and viral genes. In t his study we examined the effects of Rep78 on expression of the luciferase gene from the human cytomegalovirus immediate-early promoter in HeLa cells and on translation of RNA encoding luciferase in rabbit reticulocyte lysate . When Rep78 and luciferase were coexpressed, the luciferase activity decre ased despite increased levels of luciferase mRNA in the cells. Purified Rep 78 or Rep68 fused with Escherichia coil maltose binding protein suppressed translation of luciferase RNA in vitro, but Rep52/40 fusion proteins did no t. A mutated Rep78, which is 520 aa long and truncated at its C-terminus, d id suppress the in vitro translation, whereas a similarly truncated Rep78 o f 420 aa did not. The results indicate that Rep78/68 function to suppress g ene expression through translation inhibition, which requires the N-termina l region contained within aa 1-520. (C) 2000 Academic Press.