RNA聚合酶Ⅱ转录延伸因子

当RNA聚合酶Ⅱ(RNAPⅡ)离开启动子开始转录延伸时,会遇到包括紧密包装形成染色质的核小体在内的多种障碍,细胞内存在多种因子可协助RNAPⅡ克服这些障碍,保证转录的顺利进行。遗传和生化研究已经分离和鉴定了一些在此过程中起作用的延伸因子(elongation factor),现依据作用方式和效果对目前发现的主要延伸因子的研究进展进行了分类综述。     

BRCA2 Regulates Transcription Elongation by RNA Polymerase II to Prevent R-Loop Accumulation

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Characterization of Schizosaccharomyces pombe RNA triphosphatase

RNA triphosphatase catalyzes the first step in mRNA cap formation which entails the cleavage of the β–γ phosphoanhydride bond of triphosphate-terminated RNA to yield a diphosphate end that is then capped with GMP by RNA guanylyltransferase. Here we characterize a 303 amino acid RNA triphosphatase (Pct1p) encoded by the fission yeast Schizosaccharomyces pombe. Pct1p hydrolyzes the γ phosphate of triphosphate-terminated poly(A) in the presence of magnesium. Pct1p also hydrolyzes ATP to ADP and P_i in the presence of manganese or cobalt (K_m = 19 µM ATP; k_cat = 67 s^–1). Hydrolysis of 1 mM ATP is inhibited with increasing potency by inorganic phosphate (I_0.5 = 1 mM), pyrophosphate (I_0.5 = 0.4 mM) and tripolyphosphate (I_0.5 = 30 µM). Velocity sedimentation indicates that Pct1p is a homodimer. Pct1p is biochemically and structurally similar to the catalytic domain of Saccharomyces cerevisiae RNA triphosphatase Cet1p. Mechanistic conservation between Pct1p and Cet1p is underscored by a mutational analysis of the putative metal-binding site of Pct1p. Pct1p is functional in vivo in S.cerevisiae in lieu of Cet1p, provided that it is coexpressed with the S.pombe guanylyltransferase. Pct1p and other yeast RNA triphosphatases are completely unrelated, mechanistically and structurally, to the metazoan RNA triphosphatases, suggesting an abrupt evolutionary divergence of the capping apparatus during the transition from fungal to metazoan species.     

Purification and characterization of RNA polymerase II holoenzyme from Schizosaccharomyces pombe

We have purified the RNA polymerase II holoenzyme from Schizosaccharomyces pombe to near homogeneity. The Mediator complex is considerably smaller than its counterpart in Saccharomyces cerevisiae, containing only nine polypeptides larger than 19 kDa. Five of these Mediator subunits have been identified as the S. pombe homologs to Rgr1, Srb4, Med7, and Nut2 found in S. cerevisiae and the gene product of a previously uncharacterized open reading frame, PMC2, with no clear homologies to any described protein. The presence of Mediator in a S. pombe RNA polymerase II holoenzyme stimulated phosphorylation of the C-terminal domain by TFIIH purified from S. pombe. This stimulation was species-specific, because S. pombe Mediator could not stimulate TFIIH purified from S. cerevisiae. We suggest that the overall structure and mechanism of the Mediator is evolutionary conserved. The subunit composition, however, has evolved to respond properly to physiological signals.     

The RNA Polymerase II Factor RPAP1 Is Critical for Mediator-Driven Transcription and Cell Identity

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