[1] UNIV CALIF SAN FRANCISCO, DEPT BIOCHEM & BIOPHYS, SAN FRANCISCO, CA 94143 USA
[2] UNIV CALIF SAN FRANCISCO, DEPT STOMATOL, SAN FRANCISCO, CA 94143 USA
[3] UNIV CALIF SAN FRANCISCO, DEPT MICROBIOL, SAN FRANCISCO, CA 94143 USA
[4] UNIV WISCONSIN, DEPT BACTERIOL, MADISON, WI 53706 USA