[1] SmithKline Beecham Pharmaceut, Dept Bioinformat, Collegeville, PA 19426 USA
[2] Penn State Univ, Inst Mol Evolutionary Genet, University Pk, PA 16802 USA
[3] Penn State Univ, Dept Biol, University Pk, PA 16802 USA
[4] SmithKline Beecham Pharmaceut, Antiinfect Res Div, Dept Microbiol, Collegeville, PA 19426 USA