Kadikiran A E, Baumberg S
Mol Gen Genet. 1980;179(2):359-68. doi: 10.1007/BF00425465.
CRM+ nonsense mutations, as described for E. coli K12 lacZ, in theory permit determination of the direction of transcription of an isolated gene. In the hope of utilising this approach to confirm that the E gene of the E. coli K12 argECBH cluster is transcribed in the opposite direction from the CBH unit, 30 argE mutations were investigated immunologically and genetically. Only three, E1, E25 and E26 (which map close together towards the left-hand end of the gene), were found to be CRM+. Co-suppression of each argE mutation with known strongly polar lacZ amber, ochre and UGA mutations was looked for to distinguish missfense from nonsense argE's, Arg+ revertants being screened for Lac+ and Mel+ phenotypes. Of 16 mutations not hitherto characterised as nonsense, frameshift or large deletions, only three, E1, E25 and E26, appeared to be missense. Three of the nonsense mutations were also streptomycin suppressible. It appears, therefore, that among argE mutants so far studied the correlation between CRM+ and missense is complete, so that the projected method for determining the direction of transcription of argE could not be applied.
CRM +无义突变，如大肠杆菌K12 lacZ中所描述的，理论上允许确定一个孤立基因的转录方向。为了利用这种方法来证实大肠杆菌K12 argECBH基因簇的E基因转录方向与CBH单元相反，对30个argE突变进行了免疫学和遗传学研究。仅发现三个突变体E1、E25和E26（它们在基因的左端紧密连锁）是CRM +。研究了每个argE突变与已知的强极性lacZ琥珀突变、赭石突变和UGA突变的共抑制情况，以区分argE的错义突变与无义突变，筛选Arg +回复体的Lac +和Mel +表型。在迄今未被鉴定为无义、移码或大缺失的16个突变中，只有三个突变体E1、E25和E26似乎是错义突变。其中三个无义突变也可被链霉素抑制。因此，在迄今为止研究的argE突变体中，CRM +与错义之间的相关性是完全的，因此无法应用所设想的确定argE转录方向的方法。
