Bölker M, Kahmann R
Institut für Genbiologische Forschung Berlin GmbH, FRG.
EMBO J. 1989 Aug;8(8):2403-10. doi: 10.1002/j.1460-2075.1989.tb08370.x.
Expression of the phage Mu mom gene is transcriptionally regulated by DNA methylation. Three GATC sites upstream of the mom promoter have to be methylated by the Escherichia coli deoxyadenosine methylase (Dam) to allow initiation of transcription. An E. coli dam strain was mutagenized with Tn5 in an attempt to isolate mutants which allow mom gene expression. Three independent Tn5 mutants were isolated, each mapped to a gene at 89.6 min which we designate momR. The wildtype gene was cloned and sequenced, it encodes a protein of 305 amino acids. The protein belongs to a group of related bacterial activators recently identified as the LysR family (Henikoff et al., 1988). MomR protein was overproduced and purified. Expression of momR is autoregulated; MomR binds to a 43 bp region upstream of its coding sequence. In the mom promoter MomR protects a 43 bp region containing the three GATC sites. Specific binding to these sequences was observed only with unmethylated DNA. Fortuitously, we learned that MomR is identical to OxyR, a regulatory protein responding to oxidative stress. We discuss the implications of this control for Mu development.
噬菌体Mu的mom基因表达受DNA甲基化的转录调控。mom启动子上游的三个GATC位点必须被大肠杆菌脱氧腺苷甲基化酶（Dam）甲基化，才能启动转录。为了分离出允许mom基因表达的突变体，用Tn5对大肠杆菌dam菌株进行诱变。分离出三个独立的Tn5突变体，每个突变体都定位到89.6分钟处的一个基因，我们将其命名为momR。克隆并测序了野生型基因，它编码一个305个氨基酸的蛋白质。该蛋白质属于最近被鉴定为LysR家族的一组相关细菌激活剂（Henikoff等人，1988年）。过量表达并纯化了MomR蛋白。momR的表达是自我调节的；MomR与其编码序列上游的一个43bp区域结合。在mom启动子中，MomR保护一个包含三个GATC位点的43bp区域。仅在未甲基化的DNA上观察到与这些序列的特异性结合。幸运的是，我们发现MomR与OxyR相同，OxyR是一种对氧化应激作出反应的调节蛋白。我们讨论了这种调控对Mu发育的影响。
