Positive and negative autoregulation of the adeno-associated virus type 2 genome

Abstract

The defective human parvovirus, adeno-associated virus (AAV), requires multiple functions provided by a coinfecting helper virus for viral replication. In addition, it has recently been shown that at least one AAV gene is also required for AAV DNA replication. In this paper, we investigate the autoregulation of the AAV genome by analyzing the expression of mutant AAV genomes upon transfection into adenovirus-infected human cells. Evidence is presented which indicates that the AAV genome regulates its own gene expression in at least two ways. First, either the AAV p5 gene or both the p5 and p19 genes appear to encode a trans activator of AAV transcription. Frameshift mutations within the p5 or p19 gene severely inhibited the synthesis and accumulation of all AAV transcripts. The defective accumulation of transcripts could be complemented in trans, in a manner independent of DNA replication, by cotransfection with a capsid deletion mutant. Second, evidence is presented which suggests that the p5 and p19 genes contain negative cis-active regulatory elements. Deletion of sequences within the p5 and p19, genes enhanced the accumulation of the p5 transcript in cis upon complementation with an AAV capsid deletion mutant, whereas certain deletions enhanced p40 RNA accumulation in the absence of trans activation by the p5 gene.

The cryptic life style of adenoassociated virus

“…Of more novel aspect is a region in the middle of the rep orf (between map positions 10 and 37); this region down-regulates the expression of rep at a step after the initiation of transcription. As a consequence, the accumulation of rep transcripts is only about 10-20°/0 those of p40 transcripts (17).…”

Adeno‐Associated Virus Rep78 Binds to E2‐Responsive Element 1 of Bovine Papillomavirus Type 1

“…Alternatively, perhaps Rep78 interacts with other cellular factors for activation of BPV-1 gene expression. In the presence of aden- ovirus, Rep78 has been shown to transactivate transcription for AAV's own gene expression (21), whereas in the absence of adenovirus, all 4 Rep proteins have been observed to repress homologus expression (39). Several possible mechanisms have to be considered to explain the inhibitory effects of the Rep proteins on transcript accumulation from different heterologous and homologous promoters.…”

“…These studies have pointed to AAV Rep78 and Rep68 proteins as multifunctional proteins that process ATP-dependent helicase activity (18) and site-speci c endonuclease activity (18,19) and bind DNA covalently and non-covalently (20). Rep78 and Rep68 can also act as transcriptional activators or repressors (21,22). It has been suggested that a short DNA sequence motif, GCTC (or its complement), serves as a binding site for Rep78 and Rep68 (23).…”

Carcinogen‐induced accumulation of adeno‐associated parvovirus dna is transient as a result of two antagonistic activities that both require De Novo protein synthesis

“…Although it has been shown that initiation of carcinogen-induced AAV DNA synthesis does not require functional AAV genes (Yalkinoglu et al, 1991), its maintenance may depend on AAV-encoded proteins. In the case of AAV-2, DNA replication and gene expression are known to be subject to autoregulation by the rep gene products of the left open reading frame (Beaton et al, 1989;Berm and Bohenzky, 1987;Berns and Labow, 1987;Labow and Berns, 1988;Labow et al, 1986;Tratschin et al, 1984Tratschin et al, , 1986. Positive and negative aspects of autoregulation require the terminal repeats as targets (Beaton et al, 1989;Labow et al, 1987).…”

“…Regulation by rep proteins appears to be stimulatory when the cellular milieu is favorable for AAV production and to be inhibitory under nonpermissive conditions. For both activities the AAV terminal repeats are required as targets (Beaton et al, 1989;Berns and Bohenzky, 1987;Berns and Labow, 1987;Labow and Berns, 1988;Labow et al, 1986;Tratschin et al, 1984Tratschin et al, , 1986. Furthermore, AAV rep proteins can negatively regulate expression from heterologous promoters Mendelson et al, 1988).…”