Nowatzke W L, Richardson J P
Department of Chemistry, Indiana University, Bloomington 47405, USA.
J Biol Chem. 1996 Jan 12;271(2):742-7. doi: 10.1074/jbc.271.2.742.
A transcription termination factor (Rho) was purified from the Gram-positive bacterium Micrococcus luteus, and the complete gene sequence was determined. The M. luteus Rho polypeptide has 690 residues, which is 271 residues more than its homolog from Escherichia coli. Most of the additional residues compose a highly charged, hydrophilic segment that is inserted in a non-conserved region between two conserved regions of the RNA-binding domain of the known Rho homolog proteins. This segment extends from residues 49 to 311 and includes a stretch of 238 residues that contain no hydrophobic side chains. Biochemical studies indicate that the M. luteus protein is very similar to E. coli Rho in terms of its RNA-dependent NTPase activity and its sensitivity to the Rho-specific inhibitor bicyclomycin. However, the M. luteus protein has a less stringent RNA cofactor specificity. It also acts to terminate RNA transcription with E. coli RNA polymerase on the lambda cro DNA template, but at much earlier termination stop points than those recognized by E. coli Rho. Thus, the M. luteus protein functions as a true Rho factor, but with a different specificity than that of E. coli Rho. We propose that this altered specificity is consistent with its need to function on transcripts that have a high content of G + C residues.
从革兰氏阳性细菌藤黄微球菌中纯化出一种转录终止因子（Rho），并测定了其完整的基因序列。藤黄微球菌的Rho多肽有690个残基，比其来自大肠杆菌的同源物多271个残基。大多数额外的残基组成了一个高度带电的亲水区段，该区段插入到已知Rho同源蛋白RNA结合结构域两个保守区域之间的一个非保守区域。这个区段从第49位残基延伸到第311位残基，包括一段238个残基的序列，其中不含疏水侧链。生化研究表明，藤黄微球菌的蛋白质在其RNA依赖性NTPase活性及其对Rho特异性抑制剂双环霉素的敏感性方面与大肠杆菌的Rho非常相似。然而，藤黄微球菌的蛋白质具有不太严格的RNA辅因子特异性。它也能在λ cro DNA模板上与大肠杆菌RNA聚合酶一起终止RNA转录，但终止位点比大肠杆菌Rho识别的位点要早得多。因此，藤黄微球菌的蛋白质起着真正的Rho因子的作用，但特异性与大肠杆菌的Rho不同。我们认为这种改变的特异性与其在富含G + C残基的转录本上发挥作用的需求是一致的。
