A Novel Class of Mutants of the pilS Gene Encoding Plasmid R64 Type IV Prepilin: Interface of PilS-PilV Interactions

Department of Biology, Tokyo Metropolitan University, Minamiohsawa, Hachioji, Tokyo 192-0397, Japan

^* To whom correspondence should be addressed. Email: komano-teruya{at}c.metro-u.ac.jp.

	Abstract

The type IV pili of plasmid R64 belonging to the type IVB group are required only for liquid matings. They consist of PilS pilin and PilV adhesin as major and minor components, respectively. PilS pilin is first synthesized as a 22-kDa prepilin from the pilS gene, and is then processed to a 19-kDa mature pilin by PilU prepilin peptidase. In a previous genetic analysis, we identified four classes of the pilS mutants (T. Horiuchi, and T. Komano, J. Bacteriol. 180:4613-4620, 1998). The products of the class I pilS mutants were not processed by prepilin peptidase; the products of the class II mutants were not secreted; in the class III mutants, type IV pili with reduced activities in liquid matings were produced; and in the class IV mutants, type IV pili with normal activities were produced. Here, we describe a novel class, class V, of pilS mutants. Mutants in the pilS gene at the 56th glycine or 57th tyrosine produced type IV pili lacking PilV adhesin, which were inactive in liquid matings. The 56th and 57th residues in PilS pilin are suggested to function as an interface of PilS-PilV interactions.