Vierling S, Weber T, Wohlleben W, Muth G
Mikrobiologie/Biotechnologie, Universität Tübingen, Germany.
J Bacteriol. 2000 Jul;182(14):4005-11. doi: 10.1128/JB.182.14.4005-4011.2000.
The role of the 20,922-Da RecX protein and its interference with RecA activity were analyzed in Streptomyces lividans. The recX gene is located 220 bp downstream of recA. Transcriptional analysis by reverse transcriptase PCR demonstrated that recX and recA constitute an operon. While recA was transcribed at a basal level even under noninducing conditions, a recA-recX cotranscript was only detectable after induction of recA following DNA damage. The recA-recX cotranscript was less abundant than the recA transcript alone. The recX gene was inactivated by gene replacement. The resulting mutant had a clearly diminished colony size, but was not impaired in recombination activity, genetic instability, and resistance against UV irradiation. Expression of an extra copy of the S. lividans recA gene under control of the thiostrepton-inducible tipA promoter was lethal to the recX mutant, demonstrating that RecX is required to overcome the toxic effects of recA overexpression. Since inactivation of the recX gene did not influence transcription of recA, the putative function of the RecX protein might be the downregulation of RecA activity by interaction with the RecA protein or filament.
在淡紫链霉菌中分析了20,922道尔顿的RecX蛋白的作用及其对RecA活性的干扰。recX基因位于recA下游220 bp处。通过逆转录酶PCR进行的转录分析表明，recX和recA构成一个操纵子。虽然即使在非诱导条件下recA也以基础水平转录，但只有在DNA损伤后诱导recA后才能检测到recA-recX共转录本。recA-recX共转录本比单独的recA转录本丰度低。recX基因通过基因置换失活。所得突变体的菌落大小明显减小，但重组活性、遗传不稳定性和对紫外线照射的抗性未受损。在硫链丝菌素诱导型tipA启动子控制下表达额外拷贝的淡紫链霉菌recA基因对recX突变体是致死的，表明需要RecX来克服recA过表达的毒性作用。由于recX基因的失活不影响recA的转录，RecX蛋白的推定功能可能是通过与RecA蛋白或细丝相互作用来下调RecA活性。
