Crawford E W, Shimkets L J
Department of Microbiology, University of Georgia, Athens Georgia 30602-2605 USA.
Genes Dev. 2000 Feb 15;14(4):483-92.
Myxococcus xanthus fruiting body development is induced by amino acid limitation. The decision to grow or develop is established by the RelA-dependent stringent response and A-signaling. We identified two new members of this regulatory hierarchy, socE and the C-signaling gene csgA. SocE depletion arrests growth and induces sporulation under conditions that normally favor growth as well as curtailing DNA and stable RNA synthesis, inhibiting cell elongation, and inducing accumulations of the stringent nucleotides ppGpp and pppGpp [(p)ppGpp]. This system separates C-signaling, which does not occur under these conditions, from CsgA enzyme activity. Amino acid substitutions in the CsgA coenzyme binding pocket or catalytic site eliminate growth arrest. relA mutation also eliminates growth arrest. Eleven pseudorevertants selected for growth following SocE depletion contained mutations in csgA or relA. These results suggest that CsgA induces the stringent response and while SocE inhibits it. Unlike the csgA mutant, wild-type and socE csgA cells maintained high levels of (p)ppGpp throughout development. We suggest that CsgA maintains growth arrest throughout development to divert carbon from A-signaling and other sources into developmental macromolecular synthesis.
黄色黏球菌子实体发育由氨基酸限制诱导。生长或发育的决定由RelA依赖性严谨反应和A信号建立。我们鉴定出了这个调控层级中的两个新成员，即socE和C信号基因csgA。在通常有利于生长的条件下，SocE缺失会阻止生长并诱导孢子形成，同时减少DNA和稳定RNA合成，抑制细胞伸长，并诱导严谨核苷酸ppGpp和pppGpp [（p）ppGpp]的积累。该系统将在这些条件下不会发生的C信号与CsgA酶活性分开。CsgA辅酶结合口袋或催化位点的氨基酸取代消除了生长停滞。relA突变也消除了生长停滞。在SocE缺失后选择用于生长的11个假回复突变体在csgA或relA中含有突变。这些结果表明CsgA诱导严谨反应，而SocE抑制它。与csgA突变体不同，野生型和socE csgA细胞在整个发育过程中都维持高水平的（p）ppGpp。我们认为CsgA在整个发育过程中维持生长停滞，以将碳从A信号和其他来源转移到发育性大分子合成中。
