Computational Biology, 1100 Fairview Avenue. N. M2-B876, PO Box 19024, Seattle, WA 98109-1024, USA. zjiang@fhcrc.org|Computational Biology, 1100 Fairview Avenue. N. M2-B876, PO Box 19024, Seattle, WA 98109-1024, USA. zjiang@fhcrc.org