An extreme clockwise switch bias mutation in fliG of Salmonella typhimurium and its suppression by slow-motile mutations in motA and motB.
An extreme clockwise switch bias mutation in fliG of Salmonella typhimurium and its suppression by slow-motile mutations in motA and motB.
复制标题
鼠伤寒沙门氏菌 fliG 的极端顺时针转换偏向突变及其 motA 和 motB 慢速突变的抑制。
DOI：
10.1128/jb.179.9.2994-3003.1997
复制
发表时间：
1997
影响因子：
3.2
通讯作者：
Macnab,RM
中科院分区：
文献类型：
--
作者：
Togashi,F;Yamaguchi,S;Kihara,M;Aizawa,SI;Macnab,RM
假回复突变体（第二位点抑制突变体）分离自一组亲本突变体的沙门氏菌鞭毛开关基因fliG和fliM的缺陷。大多数抑制性突变位于染色体的鞭毛区IIIb。一个fliG突变体，SJW 2811，引起了大量的运动基因motA和motB，这是在鞭毛区II的抑制突变。SJW 2811在FliG的169至171位处具有三个氨基酸缺失（Δ Pro-Ala-Ala），其具有极端的顺时针运动偏向，其产生逆平滑游泳（即，通过流体动力学诱导的右手螺旋束的顺时针旋转游泳），并在半固体培养基上形成Mot（-）样菌落。与先前报道的反向游泳突变体不同，它没有表现出对丝氨酸的趋化反应，即使在delta che背景下也保持反向;因此，它的开关被锁定在顺时针状态。突变的位置进一步强调了先前自发错义突变体研究的结论（V.M. Irikura，M. Kihara，S.山口，H。Sockett和R. M. Macnab，J. Bacteriol. 175：802-810，1993），FliG序列的中心部分中的相对局部化的区域对于转换是至关重要的。所有的第二个位点的突变motA和motB引起一些损害的运动，无论是在假回复突变体和野生型fliG背景。通过mot突变抑制fliG突变的机制是复杂的，涉及由于电机速度降低而导致的右手鞭毛束的不稳定。MotA和MotB序列中的突变在相当大的程度上聚集如下：在MotA的跨膜螺旋3和4以及MotB的唯一跨膜螺旋中，在螺旋-膜界面处，在MotA的胞质结构域中，以及在MotB的周质结构域的肽聚糖结合区附近。的MotB序列的Lys 28和Asp 33的质子传递到扭矩产生的网站的潜在重要性进行了讨论。
Pseudorevertants (second-site suppressor mutants) were isolated from a set of parental mutants of Salmonella with defects in the flagellar switch genes fliG and fliM. Most of the suppressing mutations lay in flagellar region IIIb of the chromosome. One fliG mutant, SJW2811, gave rise to a large number of suppressor mutations in the motility genes motA and motB, which are in flagellar region II. SJW2811, which has a three-amino-acid deletion (delta Pro-Ala-Ala) at positions 169 to 171 of FliG, had an extreme clockwise motor bias that produced inverse smooth swimming (i.e., swimming by means of clockwise rotation of a hydrodynamically induced right-handed helical bundle), and formed Mot(-)-like colonies on semisolid medium. Unlike previously reported inverse-swimming mutants, it did not show a chemotactic response to serine, and it remained inverse even in a delta che background; thus, its switch is locked in the clockwise state. The location of the mutation further underscores the conclusion from a previous study of spontaneous missense mutants (V. M. Irikura, M. Kihara, S. Yamaguchi, H. Sockett, and R. M. Macnab, J. Bacteriol. 175:802-810, 1993) that a relatively localized region in the central part of the FliG sequence is critically important for switching. All of the second-site mutations in motA and motB caused some impairment of motility, both in the pseudorevertants and in a wild-type fliG background. The mechanism of suppression of the fliG mutation by the mot mutations is complex, involving destabilization of the right-handed flagellar bundle as a result of reduced motor speed. The mutations in the MotA and MotB sequences were clustered to a considerable degree as follows: in transmembrane helices 3 and 4 of MotA and the sole transmembrane helix of MotB, at helix-membrane interfaces, in the cytoplasmic domains of MotA, and in the vicinity of the peptidoglycan binding region of the periplasmic domain of MotB. The potential importance of Lys28 and Asp33 of the MotB sequence for proton delivery to the site of torque generation is discussed.