Richardson J P
Department of Chemistry, Indiana University, Bloomington 47405.
Crit Rev Biochem Mol Biol. 1993;28(1):1-30. doi: 10.3109/10409239309082571.
Chromosomes are organized into units of expression that are bounded by sites where transcription of DNA sequences into RNA is initiated and terminated. To allow for efficient stepwise assembly of complete transcripts, the transcribing enzyme (RNA polymerase) makes a stable complex with the DNA template until it reaches the terminator. Three general mechanisms of transcription termination have been recognized: one is by a spontaneous dissociation of the RNA at a sequence segment where RNA polymerase does not maintain its usual stable interaction with the nascent chain; another involves the action of a protein (rho factor in bacteria) on the nascent RNA to mediate its dissociation; and a third involves an action triggered by a protein that binds to the DNA at a sequence that is just downstream of the termination stop point. Transcription termination is important in the regulation of gene expression both by modulating the relative levels of various genes within a single unit of expression and by controlling continuation of transcription in response to a metabolic or regulatory signal.
染色体被组织成表达单位，这些单位由DNA序列转录为RNA起始和终止的位点界定。为了实现完整转录本的高效逐步组装，转录酶（RNA聚合酶）与DNA模板形成稳定复合物，直到到达终止子。转录终止已被确认有三种一般机制：一种是RNA在RNA聚合酶与新生链不保持其通常稳定相互作用的序列片段处自发解离；另一种涉及一种蛋白质（细菌中的rho因子）对新生RNA的作用以介导其解离；第三种涉及由一种蛋白质引发的作用，该蛋白质在终止位点下游的序列处与DNA结合。转录终止在基因表达调控中很重要，既可以通过调节单个表达单位内各种基因的相对水平，也可以通过响应代谢或调节信号控制转录的继续进行来实现。
