Preiser P R, Levinger L F
School of Life and Health Sciences, University of Delaware, Newark 19716.
J Biol Chem. 1991 Dec 15;266(35):23602-5.
Using an in vitro processing system, we have identified a required sequence surrounding the Drosophila melanogaster 5 S RNA processing site at nucleotide 120. Mutations in this region vary the processing rate from complete inhibition to a level equal to or greater than wild type. Analysis of mutants at +1 and in the region 118-122 separates the inhibitory effect into two parts. 1) Nucleotide 118 C, the base-paired nucleotide in helix I proximal to the processing site, plays an essential role. Changing it to a purine inhibits processing. The +1-118 base pair must be intact, but this alone is not sufficient for processing, since compensatory changes at +1 do not restore down-processing mutants at 118 to the wild type level. 2) The processing site has to be pyrimidine rich; multiple contiguous purines inhibit processing. On the other hand, multiple pyrimidines can largely negate the inhibitory effect of a mutation at position 118. Thus a base-paired C at 118 followed by a stretch of pyrimidines is the processing signal, which may be recognized by the processing enzyme and/or a required accessory factor.
利用体外加工系统，我们在果蝇5S RNA加工位点（核苷酸120处）周围确定了一个必需序列。该区域的突变会使加工速率从完全抑制到等于或高于野生型水平发生变化。对+1位点和118 - 122区域的突变体分析将抑制作用分为两部分。1）核苷酸118C，即加工位点近端螺旋I中的碱基配对核苷酸，起着至关重要的作用。将其变为嘌呤会抑制加工。+1 - 118碱基对必须完整，但仅此一点不足以进行加工，因为+1位点的补偿性变化并不能将118位点的加工缺陷突变体恢复到野生型水平。2）加工位点必须富含嘧啶；多个连续的嘌呤会抑制加工。另一方面，多个嘧啶在很大程度上可以抵消118位点突变的抑制作用。因此，118位点的碱基配对C后面跟着一段嘧啶就是加工信号，它可能被加工酶和/或所需的辅助因子识别。
