Lopez S, Livingstone-Zatchej M, Jourdain S, Thoma F, Sentenac A, Marsolier M C
Service de Biochimie et de Génétique Moléculaire, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France.
Mol Cell Biol. 2001 May;21(9):3096-104. doi: 10.1128/MCB.21.9.3096-3104.2001.
Transcription of yeast class III genes involves the formation of a transcription initiation complex that comprises RNA polymerase III (Pol III) and the general transcription factors TFIIIB and TFIIIC. Using a genetic screen for positive regulators able to compensate for a deficiency in a promoter element of the SNR6 gene, we isolated the NHP6A and NHP6B genes. Here we show that the high-mobility-group proteins NHP6A and NHP6B are required for the efficient transcription of the SNR6 gene both in vivo and in vitro. The transcripts of wild-type and promoter-defective SNR6 genes decreased or became undetectable in an nhp6ADelta nhp6BDelta double-mutant strain, and the protection over the TATA box of the wild-type SNR6 gene was lost in nhp6ADelta nhp6BDelta cells at 37 degrees C. In vitro, NHP6B specifically stimulated the transcription of SNR6 templates up to fivefold in transcription assays using either cell nuclear extracts from nhp6ADelta nhp6BDelta cells or reconstituted transcription systems. Finally, NHP6B activated SNR6 transcription in a TFIIIC-independent assay. These results indicate that besides the general transcription factors TFIIIB and TFIIIC, additional auxillary factors are required for the optimal transcription of at least some specific Pol III genes.
酵母III类基因的转录涉及转录起始复合物的形成，该复合物由RNA聚合酶III（Pol III）以及通用转录因子TFIIIB和TFIIIC组成。通过对能够补偿SNR6基因启动子元件缺陷的正向调节因子进行遗传筛选，我们分离出了NHP6A和NHP6B基因。在此我们表明，高迁移率族蛋白NHP6A和NHP6B在体内和体外都是SNR6基因高效转录所必需的。在nhp6Δ nhp6BΔ双突变菌株中，野生型和启动子缺陷型SNR6基因的转录本减少或变得无法检测到，并且在37℃时，nhp6Δ nhp6BΔ细胞中野生型SNR6基因TATA框上的保护作用丧失。在体外，使用来自nhp6Δ nhp6BΔ细胞的细胞核提取物或重组转录系统进行转录测定时，NHP6B可将SNR6模板的转录特异性刺激高达五倍。最后，在不依赖TFIIIC的测定中，NHP6B激活了SNR6转录。这些结果表明，除了通用转录因子TFIIIB和TFIIIC之外，至少某些特定的Pol III基因的最佳转录还需要其他辅助因子。
