Irikura V M, Kihara M, Yamaguchi S, Sockett H, Macnab R M
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06511.
J Bacteriol. 1993 Feb;175(3):802-10. doi: 10.1128/jb.175.3.802-810.1993.
FliG, FliM, and FliN are three proteins of Salmonella typhimurium that affect the rotation and switching of direction of the flagellar motor. An analysis of mutant alleles of FliM has been described recently (H. Sockett, S. Yamaguchi, M. Kihara, V. M. Irikura, and R. M. Macnab, J. Bacteriol. 174:793-806, 1992). We have now analyzed a large number of mutations in the fliG and fliN genes that are responsible for four different types of defects: failure to assembly flagella (nonflagellate phenotype), failure to rotate flagella (paralyzed phenotype), and failure to display normal chemotaxis as a result of an abnormally high bias to clockwise (CW) or counterclockwise (CCW) rotation (CW-bias and CCW-bias phenotypes, respectively). The null phenotype for fliG, caused by nonsense or frameshift mutations, was nonflagellate. However, a considerable part of the FliG amino acid sequence was not needed for flagellation, with several substantial in-frame deletions preventing motor rotation but not flagellar assembly. Missense mutations in fliG causing paralysis or abnormal switching occurred at a number of positions, almost all within the middle one-third of the gene. CW-bias and CCW-bias mutations tended to segregate into separate subclusters. The null phenotype of fliN is uncertain, since frameshift and nonsense mutations gave in some cases the nonflagellate phenotype and in other cases the paralyzed phenotype; in none of these cases was the phenotype a consequence of polar effects on downstream flagellar genes. Few positions in FliN were found to affect switching: only one gave rise to the CW mutant bias and only four gave rise to the CCW mutant bias. The different properties of the FliM, FliG, and FliN proteins with respect to the processes of assembly, rotation, and switching are discussed.
FliG、FliM和FliN是鼠伤寒沙门氏菌的三种蛋白质，它们影响鞭毛马达的旋转和方向转换。最近已有关于FliM突变等位基因的分析报道（H. 索基特、S. 山口、M. 木原、V. M. 伊里库拉和R. M. 麦克纳布，《细菌学杂志》174:793 - 806，1992年）。我们现在分析了fliG和fliN基因中的大量突变，这些突变导致四种不同类型的缺陷：无法组装鞭毛（无鞭毛表型）、无法旋转鞭毛（麻痹表型）以及由于顺时针（CW）或逆时针（CCW）旋转的异常高偏向性而无法表现出正常趋化性（分别为CW偏向和CCW偏向表型）。由无义或移码突变导致的fliG无效表型为无鞭毛。然而，鞭毛形成并不需要FliG氨基酸序列的相当一部分，有几个相当大的框内缺失会阻止马达旋转但不影响鞭毛组装。fliG中导致麻痹或异常转换的错义突变发生在多个位置，几乎都在基因的中间三分之一区域内。CW偏向和CCW偏向突变倾向于分离成不同的亚簇。fliN的无效表型不确定，因为移码和无义突变在某些情况下产生无鞭毛表型，在其他情况下产生麻痹表型；在这些情况中，没有一种表型是对下游鞭毛基因的极性效应的结果。发现FliN中很少有位置影响转换：只有一个导致CW突变偏向，只有四个导致CCW突变偏向。本文讨论了FliM、FliG和FliN蛋白质在组装、旋转和转换过程中的不同特性。
