REGULATION OF PAP PILIN PHASE VARIATION BY A MECHANISM INVOLVING DIFFERENTIAL DAM METHYLATION STATES
REGULATION OF PAP PILIN PHASE VARIATION BY A MECHANISM INVOLVING DIFFERENTIAL DAM METHYLATION STATES
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DOI：
10.1002/j.1460-2075.1990.tb07626.x
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发表时间：
1990-12-01
期刊：
影响因子：
11.4
通讯作者：
LOW, DA
中科院分区：
文献类型：
--
作者：
BLYN, LB;BRAATEN, BA;LOW, DA
大肠杆菌中pap蛋白（papA）基因的转录受一种可遗传的相位变异机制控制，在这种机制中，转录活性（相位开启）和非活性（相位关闭）状态之间发生交替。我们的研究结果表明，pap DNA序列在没有DNA重排的情况下发生了相转换，这将该系统与大肠杆菌1型毛和沙门氏菌鞭毛相变化区分出来。对断相和开相dna中papA上游调控区域的分析表明，存在两个脱氧腺苷甲基化酶（Dam）位点GATC1028和GATC1130。DNA的MboI和DpmI限制性酶切的Southern blot分析显示，GATC1028位点仅在从相群分离的DNA中未甲基化。相反，从相离群体中分离的DNA中GATC1130位点未甲基化。未甲基化的GATC位点在大肠杆菌中的存在是不寻常的，据我们所知，以前没有报道过。这些结果表明GATC1028和GATC1130的甲基化状态可能调控pap转录。与这一假设一致，Dam甲基化酶水平影响pap转录的调节；在大肠杆菌中没有papA转录。此外，在表达异常高水平Dam的大肠杆菌中没有观察到从相位关闭到相位打开状态的转变。提出了一个基本模型，概述了一种可能的机制，通过这种机制，甲基化状态可能发生相关闭和相打开之间的交替。
Transcription of the pap pilin (papA) gene in Escherichia coli is subject to control by a heritable phase variation mechanism in which alternation between transcriptionally active (phase on) and inactive (phase off) states occurs. Our results suggest that phase switching occurs without DNA rearrangement of pap DNA sequences, distinguishing this system from those described for E. coli type 1 pili and Salmonella flagellar phase variation. Analysis of the regulatory region upstream of papA in DNAs isolated from phase off and phase on cell populations showed that two deoxyadenosine methylase (Dam) sites, GATC1028 and GATC1130, were present. Southern blot analysis of MboI and DpmI restriction digests of DNAs showed that the GATC1028 site was unmethylated only in DNA isolated from phase on populations. Conversely, GATC1130 sites were unmethylated in DNA isolated from phase off populations. The presence of unmethylated GATC sites in E. coli unusual and to our knowledge has not been previously reported. These results suggest that the methylation states of GATC1028 and GATC1130 may regulate pap transcription. Consistent with this hypothesis, Dam methylase levels affected the regulation of pap transcription; papA transcription was absent in dam- E. coli. Moreover, transition from the phase off to phase on state was not observed in E. coli expressing aberrantly high levels of Dam. A basic model is presented which outline a possible mechanism by which alternation between phase off and phase on methylation states could occur.