Steele M I, Lorenz D, Hatter K, Park A, Sokatch J R
Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City 73190.
J Biol Chem. 1992 Jul 5;267(19):13585-92.
A 5417-base pair (bp) region of Pseudomonas aeruginosa PAO chromosomal DNA containing the mmsAB operon and an upstream regulatory gene (mmsR) has been cloned and characterized. The operon contains two structural genes involved in valine metabolism: mmsA, which encodes methylmalonate-semialdehyde dehydrogenase; and mmsB, which encodes 3-hydroxyisobutyrate dehydrogenase. mmsA and mmsB share the same orientation and are separated by a 16-bp noncoding region. The transcriptional start site for the operon has been pinpointed to a cytidine residue located 77 bp from the translational start site of the operon. mmsR is located on the opposite strand and begins 134 bp from the translational start site of mmsA. MmsR has been identified as a member of the XylS/AraC family of transcriptional regulators and appears to act as a positive regulator of the mmsAB operon. Sequence comparison of MmsA to other proteins in the data bases revealed that MmsA belongs to the aldehyde dehydrogenase (NAD+) superfamily. MmsB shares a 44% amino acid identity with 3-hydroxyisobutyrate dehydrogenase from rat liver. Mutants with insertionally inactivated mmsR, mmsA, and mmsB grow slowly on valine/isoleucine medium and exhibit reduced enzyme activity in cell-free extracts compared to P. aeruginosa PAO.
已克隆并鉴定了铜绿假单胞菌PAO染色体DNA中一个包含mmsAB操纵子和一个上游调控基因（mmsR）的5417碱基对（bp）区域。该操纵子包含两个参与缬氨酸代谢的结构基因：mmsA，编码甲基丙二酸半醛脱氢酶；以及mmsB，编码3-羟基异丁酸脱氢酶。mmsA和mmsB方向相同，被一个16 bp的非编码区域隔开。该操纵子的转录起始位点已确定为一个胞嘧啶残基，位于该操纵子翻译起始位点77 bp处。mmsR位于相反链上，从mmsA的翻译起始位点开始134 bp处。MmsR已被鉴定为转录调节因子XylS/AraC家族的成员，似乎作为mmsAB操纵子的正调节因子发挥作用。将MmsA与数据库中的其他蛋白质进行序列比较发现，MmsA属于醛脱氢酶（NAD+）超家族。MmsB与大鼠肝脏的3-羟基异丁酸脱氢酶有44%的氨基酸同一性。与铜绿假单胞菌PAO相比，mmsR、mmsA和mmsB插入失活的突变体在缬氨酸/异亮氨酸培养基上生长缓慢，并且在无细胞提取物中酶活性降低。
