Differential Expression of over 60 Chromosomal Genes in Escherichia coli by Constitutive Expression of MarA

In Escherichia coli, the MarA protein controls expression of multiple chromosomal genes affecting resistance to antibiotics and other environmental hazards. For a more-complete characterization of the mar regulon, duplicate macroarrays containing 4,290 open reading frames of the E. coli genome were hybridized to radiolabeled cDNA populations derived from mar-deleted and mar-expressing E. coli. Strains constitutively expressing MarA showed altered expression of more than 60 chromosomal genes: 76% showed increased expression and 24% showed decreased expression. Although some of the genes were already known to be MarA regulated, the majority were newly determined and belonged to a variety of functional groups. Some of the genes identified have been associated with iron transport and metabolism; other genes were previously known to be part of the soxRS regulon. Northern blot analysis of selected genes confirmed the results obtained with the macroarrays. The findings reveal that the mar locus mediates a global stress response involving one of the largest networks of genes described.

在大肠杆菌（Escherichia coli）中，MarA蛋白可调控多种染色体基因的表达，这些基因与细菌对抗生素及其他环境危害的抗性密切相关。为更全面地表征mar调节子（mar regulon），研究人员将包含大肠杆菌基因组4290个开放阅读框的重复宏观基因阵列，与源自MarA基因敲除和MarA表达型大肠杆菌的放射性标记cDNA群体进行杂交实验。结果显示，组成型表达MarA的菌株中，超过60个染色体基因的表达发生改变：其中76%的基因表达上调，24%的基因表达下调。尽管部分基因此前已被证实受MarA调控，但绝大多数均为新鉴定的靶基因，且分属多种功能类群。本次鉴定出的部分基因与铁转运及代谢相关；另有部分基因此前已知属于soxRS调节子（soxRS regulon）。针对筛选基因的Northern印迹（Northern blot）分析验证了宏观基因阵列的实验结果。本研究结果表明，mar基因座介导了一种全局性应激响应，其所涉及的基因网络是目前已报道的最大基因调控网络之一。