Ambulos N P, Mongkolsuk S, Lovett P S
Mol Gen Genet. 1985;199(1):70-5. doi: 10.1007/BF00327512.
The plasmid gene cat-86 specifies chloramphenicol-inducible, chloramphenicol acetyltransferase in Bacillus subtilis. The inducible regulation is independent of the promoter that is used to activate cat-86 and is independent of the cat-86 coding sequence. We have proposed that the regulation of cat-86 results from the transcription of a pair of inverted-repeat sequences that immediately precede the coding sequence. These transcripts are predicted to sequester the cat-86 ribosome binding site in a stable RNA stem-loop which, in theory, should block the ribosome binding site from pairing with 16S rRNA. Inducible expression of cat-86 may therefore result in part from regulation of the translation of cat-86 mRNA. However, chloramphenicol-induction correlates with increased levels of cat-86 mRNA and the RNA stem-loop preceding the cat-86 coding sequence structurally resembles a rho-independent transcription terminator. We have therefore tested the inverted-repeats as a potential site of transcription termination. Transcription studies performed in vitro using SP6 RNA polymerase and in vivo by S1 mapping demonstrate that a substantial fraction of the potential cat-86 transcripts terminate at a site immediately 3' to the inverted-repeats. The results of the in vivo experiments suggest that the termination signal may be partially relieved by growth of cells in chloramphenicol.
质粒基因cat - 86在枯草芽孢杆菌中编码氯霉素诱导型氯霉素乙酰转移酶。这种诱导型调控独立于用于激活cat - 86的启动子，也独立于cat - 86编码序列。我们提出，cat - 86的调控源于紧接编码序列之前的一对反向重复序列的转录。这些转录本预计会在一个稳定的RNA茎环中隔离cat - 86核糖体结合位点，理论上，这应该会阻止核糖体结合位点与16S rRNA配对。因此，cat - 86的诱导型表达可能部分源于对cat - 86 mRNA翻译的调控。然而，氯霉素诱导与cat - 86 mRNA水平的增加相关，并且cat - 86编码序列之前的RNA茎环在结构上类似于一个不依赖ρ因子的转录终止子。因此，我们测试了反向重复序列作为潜在转录终止位点的可能性。使用SP6 RNA聚合酶在体外进行的转录研究以及通过S1作图在体内进行的研究表明，相当一部分潜在的cat - 86转录本在紧接反向重复序列3'端的位点终止。体内实验结果表明，细胞在氯霉素中生长可能会部分解除终止信号。
