Zhu H, Roy A L, Roeder R G, Prywes R
Department of Biological Sciences, Columbia University, New York, NY 10027.
New Biol. 1991 May;3(5):455-64.
Serum response factor (SRF), a transcription factor that binds to the serum response element (SRE) of the c-fos proto-oncogene, activates transcription of an SRE-containing reporter plasmid in vitro. We describe here preincubation experiments which indicate that SRF activates transcription by facilitating the formation of active preinitiation complexes. Full activation by SRF occurred if SRF was preincubated with the general transcription factors. However, if the general transcription factors were preincubated and SRF was added subsequently, only poor activation of transcription was observed. This suggests that SRF must be present during preinitiation complex formation and that this complex is refractory to activation if SRF is absent during its formation. We have fractionated the general transcription factors and found that only a highly purified fraction containing the TATA-binding factor TFIID (and other unidentified components) must be present during preincubation for maximal transcriptional induction by SRF. This supports a model in which SRF activates transcription by affecting the conformation of TFIID bound to the promoter. Also of interest was the finding that recombinant human TFIID expressed in bacteria cannot mediate SRF-activated transcription, although it does support basal transcription. These results suggest that SRF may affect TFIID via a cofactor or coactivator.
血清反应因子（SRF）是一种与原癌基因c-fos的血清反应元件（SRE）结合的转录因子，它能在体外激活含SRE的报告质粒的转录。我们在此描述了预孵育实验，这些实验表明SRF通过促进活性起始前复合物的形成来激活转录。如果SRF与通用转录因子预孵育，则会发生SRF的完全激活。然而，如果先预孵育通用转录因子，随后再添加SRF，则仅观察到较差的转录激活。这表明SRF必须在起始前复合物形成过程中存在，并且如果在其形成过程中不存在SRF，该复合物就难以被激活。我们对通用转录因子进行了分级分离，发现只有在预孵育过程中存在含有TATA结合因子TFIID（以及其他未鉴定成分）的高度纯化级分，SRF才能实现最大程度的转录诱导。这支持了一种模型，即SRF通过影响与启动子结合的TFIID的构象来激活转录。同样有趣的是，尽管在细菌中表达的重组人TFIID确实支持基础转录，但它不能介导SRF激活的转录。这些结果表明，SRF可能通过辅因子或共激活因子影响TFIID。
