Yamanaka K, Ogura T, Koonin E V, Niki H, Hiraga S
Department of Molecular Cell Biology, Kumamoto University School of Medicine, Japan.
Mol Gen Genet. 1994 Apr;243(1):9-16. doi: 10.1007/BF00283870.
We have isolated and characterized two multicopy suppressors, mssA and mssB, which suppress the cold-sensitive growth phenotype of the smbA2 mutant of Escherichia coli. The mssA gene is located immediately upstream of the rpsA gene (20.5 min). MssA protein was found to be related to nucleoside monophosphate kinases. The mssB gene was found to be identical to the deaD gene (69 min), which encodes a putative RNA helicase. The SmbA protein belongs to the aspartokinase family and probably represents a new, fourth aspartokinase species in E. coli. Expression of the smbA gene is essential for cell growth. The smbA2 mutant shows a pleiotropic phenotype characterized by cold-sensitive growth, hypersensitivity to the detergent sodium dodecyl sulfate, and formation of a translucent segment at midcell or at a pole of the cell when grown at 22 degrees C. In addition, some cellular proteins were either increased or decreased in amount in the smbA2 mutant. SmbA may be a regulatory factor in the expression of a battery of genes. MssA and MssB might also relate to the expression of some of these genes. Multiple copies mssA and mssB suppressed the various phenotypic features of the smbA2 mutant to various extents, suppressing the cold-sensitive growth completely.
我们已经分离并鉴定了两个多拷贝抑制子，mssA和mssB，它们可抑制大肠杆菌smbA2突变体的冷敏感生长表型。mssA基因位于rpsA基因（20.5分钟处）的紧邻上游。发现MssA蛋白与核苷单磷酸激酶相关。发现mssB基因与deaD基因（69分钟处）相同，deaD基因编码一种假定的RNA解旋酶。SmbA蛋白属于天冬氨酸激酶家族，可能代表大肠杆菌中一种新的、第四个天冬氨酸激酶种类。smbA基因的表达对细胞生长至关重要。smbA2突变体表现出多效性表型，其特征为冷敏感生长、对去污剂十二烷基硫酸钠过敏，以及在22℃生长时在细胞中部或细胞一极形成半透明区段。此外，smbA2突变体中一些细胞蛋白的量要么增加要么减少。SmbA可能是一系列基因表达中的一个调节因子。MssA和MssB可能也与其中一些基因的表达有关。多拷贝的mssA和mssB在不同程度上抑制了smbA2突变体的各种表型特征，完全抑制了冷敏感生长。
