Tønjum T, Freitag N E, Namork E, Koomey M
Kaptein W. Wilhelmsen og Frues Bakteriologiske Institutt, Rikshospitalet (National Hospital), University of Oslo, Norway.
Mol Microbiol. 1995 May;16(3):451-64. doi: 10.1111/j.1365-2958.1995.tb02410.x.
Expression of type IV pili appears to be a requisite determinant of infectivity for the strict human pathogens Neisseria gonorrhoeae and Neisseria meningitidis. The assembly of these colonization factors is a complex process. This report describes a new pilus-assembly gene, pilG, that immediately precedes the gonococcal (Gc) pilD gene encoding the pre-pilin leader peptidase. The nucleotide sequence of this region revealed a single complete open reading frame whose derived polypeptide displayed significant identities to the pilus-assembly protein PilC of Pseudomonas aeruginosa and other polytopic integral cytoplasmic membrane constituents involved in protein export and competence. A unique polypeptide of M(r) 38 kDa corresponding to the gene product was identified. A highly related gene and flanking sequences were cloned from a group B polysaccharide-producing strain of N. meningitidis (Mc). The results indicate that the pilG genes and genetic organization at these loci in Gc and Mc are extremely conserved. Hybridization studies strongly suggest that pilG-related genes exist in commensal Neisseria species and other species known to express type IV pili. Defined genetic lesions were created by using insertional and transposon mutagenesis and moved into the Gc and Mc chromosomes by allelic replacement. Chromosomal pilG insertion mutants were devoid of pili and displayed dramatically reduced competence for transformation. These findings could not be ascribed to pilin-gene alterations or to polarity exerted on pilD expression. The results indicated that PilG exerts its own independent role in neisserial pilus biogenesis.
IV型菌毛的表达似乎是淋病奈瑟菌和脑膜炎奈瑟菌这两种严格的人类病原体感染性的必要决定因素。这些定植因子的组装是一个复杂的过程。本报告描述了一个新的菌毛组装基因pilG，它紧挨着编码菌毛前体蛋白前导肽酶的淋病奈瑟菌（Gc）pilD基因。该区域的核苷酸序列揭示了一个单一的完整开放阅读框，其推导的多肽与铜绿假单胞菌的菌毛组装蛋白PilC以及其他参与蛋白质输出和感受态的多跨膜整合细胞质膜成分具有显著的同源性。鉴定出了一个与该基因产物相对应的38 kDa的独特多肽。从一株产生B群多糖的脑膜炎奈瑟菌（Mc）中克隆了一个高度相关的基因及其侧翼序列。结果表明，Gc和Mc中这些位点的pilG基因和遗传组织极其保守。杂交研究强烈表明，共生奈瑟菌属物种和其他已知表达IV型菌毛的物种中存在与pilG相关的基因。通过插入诱变和转座子诱变产生了明确的基因损伤，并通过等位基因替换将其导入Gc和Mc染色体。染色体pilG插入突变体没有菌毛，转化能力显著降低。这些发现不能归因于菌毛蛋白基因的改变或对pilD表达施加的极性。结果表明，PilG在奈瑟菌菌毛生物合成中发挥着自身独立的作用。
