IBM Computational Biology Center, P.O. Box 218, Yorktown Heights, NY 10598, USA. pdu@us.ibm.com|IBM Computational Biology Center, P.O. Box 218, Yorktown Heights, NY 10598, USA. pdu@us.ibm.com|IBM Computational Biology Center, P.O. Box 218, Yorktown Heights, NY 10598, USA. pdu@us.ibm.com|IBM Computational Biology Center, P.O. Box 218, Yorktown Heights, NY 10598, USA. pdu@us.ibm.com|IBM Computational Biology Center, P.O. Box 218, Yorktown Heights, NY 10598, USA. pdu@us.ibm.com|IBM Computational Biology Center, P.O. Box 218, Yorktown Heights, NY 10598, USA. pdu@us.ibm.com