Finlay B B, Frost L S, Paranchych W
J Bacteriol. 1984 Oct;160(1):402-7. doi: 10.1128/jb.160.1.402-407.1984.
ColB2 is a colicin-producing, 96-kilobase plasmid which encodes a conjugative system that is similar, but not identical, to F. A restriction map of this plasmid was generated, and DNA homology studies between F and ColB2 plasmids revealed homology only between their transfer operons. The locations of the ColB2 transfer operon and ColB2 pilin gene were localized on this restriction map. The gene encoding ColB2 pilin, traA, was cloned and sequenced. The pilin protein of ColB2 is identical to F, except at the amino terminus, where ala-gln of ColB2 pilin corresponds to Ala-Gly-Ser-Ser of F pilin. This is due to a 6-base-pair deletion in the ColB2 pilin gene. Biochemical studies on tryptic peptides derived from ColB2 pilin demonstrate the location of this gene to be correct. There is a putative signal peptidase cleavage site after the sequence Ala-Met-Ala, giving a signal peptide of 51 amino acids and a mature pilin protein of 68 amino acids (7,000 daltons). The amino terminus is blocked, probably with an acetyl group. A chimera containing the ColB2 pilin gene was able to complement an F traA mutant, demonstrating that the pilus assembly proteins of F can utilize the ColB2 pilin protein to form a pilus.
ColB2是一种产生大肠杆菌素的96千碱基质粒，它编码一种与F质粒相似但不相同的接合系统。构建了该质粒的限制酶切图谱，F质粒与ColB2质粒之间的DNA同源性研究表明，它们仅在转移操纵子之间存在同源性。ColB2转移操纵子和ColB2菌毛蛋白基因的位置定位在这一限制酶切图谱上。编码ColB2菌毛蛋白的基因traA被克隆并测序。ColB2菌毛蛋白与F菌毛蛋白相同，只是在氨基末端不同，ColB2菌毛蛋白的丙氨酸-谷氨酰胺对应于F菌毛蛋白的丙氨酸-甘氨酸-丝氨酸-丝氨酸。这是由于ColB2菌毛蛋白基因中发生了6个碱基对的缺失。对来自ColB2菌毛蛋白的胰蛋白酶肽段进行的生化研究证明该基因的定位是正确的。在丙氨酸-甲硫氨酸-丙氨酸序列之后有一个假定的信号肽酶切割位点，产生一个51个氨基酸的信号肽和一个68个氨基酸（7000道尔顿）的成熟菌毛蛋白。氨基末端被封闭，可能被乙酰基封闭。一个含有ColB2菌毛蛋白基因的嵌合体能够互补F traA突变体，这表明F的菌毛组装蛋白可以利用ColB2菌毛蛋白形成菌毛。
