MOLECULAR-GENETIC ANALYSIS OF THE MOA OPERON OF ESCHERICHIA-COLI K-12REQUIRED FOR MOLYBDENUM COFACTOR BIOSYNTHESIS

A 3.2 kb chromosomal DNA fragment which complements the defects in a s eries of twelve moa::Mucts insertion mutants has been sequenced. Five open reading frames (ORFs) were identified and these are arranged in a manner consistent with their forming an operon. The encoded proteins (MoaA-MoaE) have predicted molecular weights of 37 346, 18 665, 17 234 , 8843 and 16981 respectively. Examination of subclones of the whole l ocus in an expression system demonstrated the predicted products. N-te rminal amino acid sequences for the moaA, B, C and E products confirme d the translational starts. Genetic analysis distinguished four classe s of moa mutants corresponding to genes moaA, C, D and E. Potential pr omoter sequences upstream of moaA and a possible transcription termina tion signal have been identified. Genetic analysis of the chlA1 and ch lM mutants, which have been biochemically characterized as defective i n molybdopterin biosynthesis, indicates that these carry lesions in mo aA and moaD respectively. The moa locus is orientated clockwise at 17. 7 minutes in the chromosome.