Mills D R, Dobkin C, Kramer F R
Cell. 1978 Oct;15(2):541-50. doi: 10.1016/0092-8674(78)90022-3.
Q beta replicase polymerizes MDV-1 RNA at a markedly variable rate. Electrophoretic analyses of partially synthesized strands showed that a few of the elongation intermediates are much more abundant than others, reflecting a variable rate of chain elongation. Our data suggest that at a relatively small number of specific sites in the sequence of this RNA, the progress of the replicase is temporarily interrupted, and then resumes spontaneously, with a finite probability. Since the time spent between these pause sites is negligible compared with the time spent at pause sites, the mean time of chain elongation is well approximated by the sum of the mean times spent at each pause site. Nucleotide sequence analysis of the most prominent elongation intermediates indicated that they all have the potential to form a 3' terminal hairpin structure. This suggests that the marked variability in the rate of chain elongation is due to the formation of terminal hairpins in the product strand, or the reformation of hairpins in the template strand. A survey of the literature shows that this phenomenon occurs with most, if not all, nucleic acid polymerases. Structure-induced pauses may play a role in the regulation of nucleic acid synthesis.
Qβ复制酶以明显可变的速率聚合MDV-1 RNA。对部分合成链的电泳分析表明，一些延伸中间体比其他中间体丰富得多，这反映了链延伸速率的变化。我们的数据表明，在该RNA序列中相对少量的特定位点处，复制酶的进展会暂时中断，然后以一定概率自发恢复。由于与在暂停位点所花费的时间相比，这些暂停位点之间所花费的时间可以忽略不计，链延伸的平均时间可以很好地近似为在每个暂停位点所花费的平均时间之和。对最突出的延伸中间体的核苷酸序列分析表明，它们都有可能形成3'末端发夹结构。这表明链延伸速率的显著变化是由于产物链中末端发夹的形成，或者模板链中发夹的重新形成。对文献的调查表明，这种现象在大多数（如果不是全部）核酸聚合酶中都会发生。结构诱导的暂停可能在核酸合成的调控中起作用。
