REPRESSION IN-VITRO, BY HUMAN ADENOVIRUS E1A PROTEIN DOMAINS, BASAL OR TAT-ACTIVATED TRANSCRIPTION OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 LONG TERMINAL REPEAT

Human adenovirus E1A proteins can repress the expression of several vi ral and cellular genes. By using a cell-free transcription system, we demonstrated that the gene product of the E1A 12S mRNA, the 243-residu e protein E1A243R, inhibits basal transcription from the human immunod eficiency virus type 1 (HIV-1) long terminal repeat (LTR). The HIV-1 t ransactivator protein Tat greatly stimulates transcription from the vi ral promoter in vitro. However, E1A243R can repress Tat-activated tran scription in vitro. Strong repression of both basal and Tat-activated transcriptions requires only E1A N-terminal amino acid residues 1 to 8 0. Deletion analysis showed that E1A N-terminal amino acids 4 to 25 ar e essential for repression, whereas amino acid residues 30 to 49 and 7 0 to 80 are dispensable. Transcriptional repression by E1A in the cell -free transcription system is promoter specific, since under identical conditions, transcription of the adenovirus major late promoter and t he Rous sarcoma virus LTR promoter was unaffected, The repression of t ranscription by small EIA peptides in vitro provides an assay for inve stigation of molecular mechanisms governing E1A mediated repression of both basal and Tat-activated transcriptions of the HIV-1 LTR promoter .