Mermod N, Williams T J, Tjian R
Department of Biochemistry, University of California, Berkeley 94720.
Nature. 1988 Apr 7;332(6164):557-61. doi: 10.1038/332557a0.
The simian virus 40 (SV40) transcriptional enhancer is composed of multiple cis-acting DNA sequence motifs, each individually having a two- to fourfold effect on the efficiency of transcription. When various distinct cis-elements act in combination, however, a dramatic enhancement of transcription initiation often results. SV40-enhancer A-domain sequences were previously shown to be important for early and late transcription in vivo. Here we report the isolation of the enhancer binding factor AP-4, which recognizes a motif in this domain. Purified AP-4 activates SV40 late transcription in vitro, and this stimulation is augmented by the addition of transcription factor AP-1 which binds to adjacent sequences in the A-domain, suggesting coordinate action of the two factors for transcriptional enhancement. AP-1 also represses late transcription from a major in vitro start site which is poorly used in vivo, indicating that AP-1 can act as both a positive and negative regulator of SV40 late transcription. Thus by manipulating the levels of different trans-acting factors in vitro, we can recreate the pattern of SV40 late initiation observed during the viral lytic cycle in vivo.
猿猴病毒40（SV40）转录增强子由多个顺式作用DNA序列基序组成，每个基序对转录效率都有两到四倍的影响。然而，当各种不同的顺式元件联合作用时，常常会导致转录起始的显著增强。SV40增强子A结构域序列先前已被证明对体内早期和晚期转录很重要。在此我们报告增强子结合因子AP - 4的分离，它识别该结构域中的一个基序。纯化的AP - 4在体外激活SV40晚期转录，并且通过添加与A结构域中相邻序列结合的转录因子AP - 1，这种刺激作用增强，这表明这两种因子在转录增强方面存在协同作用。AP - 1还抑制来自一个在体外主要起始位点的晚期转录，该位点在体内很少被利用，这表明AP - 1可以作为SV40晚期转录的正调控因子和负调控因子。因此，通过在体外操纵不同反式作用因子的水平，我们可以重现体内病毒裂解周期中观察到的SV40晚期起始模式。
