TRANSFERASE, DNA-DIRECTED RNA POLYMERASE, STRUCTURAL GENOMICS, PSI, MCSG, PROTEIN STRUCTURE INITIATIVE, MIDWEST CENTER FOR STRUCTURAL GENOMICS, NUCLEOTIDYLTRANSFERASE, TRANSCRIPTION 3E7H THE CRYSTAL STRUCTURE OF THE BETA SUBUNIT OF THE DNA- DIRECTED RNA POLYMERASE FROM VIBRIO CHOLERAE O1 BIOVAR ELTOR