Kaplan C D, Morris J R, Wu C, Winston F
Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA.
Genes Dev. 2000 Oct 15;14(20):2623-34. doi: 10.1101/gad.831900.
The Spt4, Spt5, and Spt6 proteins are conserved throughout eukaryotes and are believed to play critical and related roles in transcription. They have a positive role in transcription elongation in Saccharomyces cerevisiae and in the activation of transcription by the HIV Tat protein in human cells. In contrast, a complex of Spt4 and Spt5 is required in vitro for the inhibition of RNA polymerase II (Pol II) elongation by the drug DRB, suggesting also a negative role in vivo. To learn more about the function of the Spt4/Spt5 complex and Spt6 in vivo, we have identified Drosophila homologs of Spt5 and Spt6 and characterized their localization on Drosophila polytene chromosomes. We find that Spt5 and Spt6 localize extensively with the phosphorylated, actively elongating form of Pol II, to transcriptionally active sites during salivary gland development and upon heat shock. Furthermore, Spt5 and Spt6 do not colocalize widely with the unphosphorylated, nonelongating form of Pol II. These results strongly suggest that Spt5 and Spt6 play closely related roles associated with active transcription in vivo.
Spt4、Spt5和Spt6蛋白在整个真核生物中都是保守的，并且被认为在转录过程中发挥关键且相关的作用。它们在酿酒酵母的转录延伸以及人类细胞中HIV Tat蛋白对转录的激活过程中具有积极作用。相比之下，在体外，药物DRB抑制RNA聚合酶II（Pol II）延伸需要Spt4和Spt5的复合物，这也表明其在体内具有消极作用。为了更深入了解Spt4/Spt5复合物和Spt6在体内的功能，我们鉴定了果蝇中Spt5和Spt6的同源物，并对它们在果蝇多线染色体上的定位进行了表征。我们发现，在唾液腺发育期间以及热休克时，Spt5和Spt6与磷酸化的、处于活跃延伸状态的Pol II广泛共定位在转录活性位点。此外，Spt5和Spt6与未磷酸化的、非延伸状态的Pol II没有广泛共定位。这些结果强烈表明，Spt5和Spt6在体内与活跃转录相关的过程中发挥密切相关的作用。
