Reines D
Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322.
J Biol Chem. 1992 Feb 25;267(6):3795-800.
In addition to polynucleotide polymerization, DNA polymerases and bacterial RNA polymerase can also remove nucleotides from the growing end of nucleic acid chains. For DNA polymerases this activity is an important factor in establishing fidelity in DNA synthesis. This report describes a novel in vitro activity of RNA polymerase II whereby it cleaves an RNA chain contained within an active elongation complex. These elongation complexes are arrested at a previously identified, naturally occurring transcriptional pause site in a human gene. The new 3'-end revealed by this cleavage remains associated with an active elongation complex and is capable of being extended by RNA polymerase II. Nascent RNA cleavage is evident after removal of free nucleotides and is dependent upon a divalent metal cation and transcription elongation factor SII. This function of SII could be important in its function as an activator of transcription elongation. It is also possible that the transcript cleavage activity of RNA polymerase II represents a proofreading function of the enzyme.
除了多核苷酸聚合作用外，DNA聚合酶和细菌RNA聚合酶还能从核酸链的生长末端去除核苷酸。对于DNA聚合酶来说，这种活性是确保DNA合成保真度的一个重要因素。本报告描述了RNA聚合酶II的一种新的体外活性，即它能切割活性延伸复合物中包含的RNA链。这些延伸复合物在人类基因中一个先前已确定的天然转录暂停位点处停滞。这种切割所揭示的新的3'末端仍与活性延伸复合物相关联，并能够被RNA聚合酶II延伸。去除游离核苷酸后，新生RNA切割很明显，并且依赖于二价金属阳离子和转录延伸因子SII。SII的这种功能在其作为转录延伸激活剂的功能中可能很重要。RNA聚合酶II的转录物切割活性也有可能代表该酶的校对功能。
