NUCLEOTIDE-SEQUENCE OF A PSEUDOMONAS-DENITRIFICANS 5.4-KILOBASE DNA FRAGMENT CONTAINING 5 COB GENES AND IDENTIFICATION OF STRUCTURAL GENES ENCODING S-ADENOSYL-L-METHIONINE - UROPORPHYRINOGEN-III METHYLTRANSFERASE AND COBYRINIC ACID A,C-DIAMIDE SYNTHASE

A 5.4-kilobase DNA fragment carrying Pseudomonas dentrificans cob genes has been sequenced. The nucleotide sequence and genetic analysis revealed that this fragment carries five different cob genes (cobA to cobE). Four of these genes present the characteristics of translationally coupled genes. cobA has been identified as the structural gene of S-adenosyl-L-methionine:uroporphyrinogen III methyltransferase (SUMT) because the encoded protein has the same NH2 terminus and molecular weight as those determined for the purified SUMT. For the same reasons the cobB gene was shown to be the structural gene for cobyrinic acid a,c-diamide synthase. Genetic and biochemical data concerning cobC and cobD mutants suggest that the products of these genes are involved in the conversion of cobyric acid to cobinamide.