THE AZOTOBACTER-VINELANDII ALG8 AND ALG44 GENES ARE ESSENTIAL FOR ALGINATE SYNTHESIS AND CAN BE TRANSCRIBED FROM AN ALGD-INDEPENDENT PROMOTER

A 2.8-kb DNA region, located immediately downstream of algD, contains the A. vinelandii alg8 and alg44 genes, whose sequences are highly hom ologous to those of the corresponding Pseudomonas aeruginosa genes. Th ese genes occur on a transcript that does not include algD, and are tr anscribed from a promoter different from that transcribing algD; this is the fourth promoter described within the alginate biosynthetic gene cluster. alg8 and alg44 mutants were constructed and shown to be comp letely impaired in alginate production. Alg8 shares 28.20% identity an d 38.09% similarity to Azorhizobium caulinodans NodC, a glycosyl trans ferase catalyzing the formation of beta-1,4 linkages. A topological mo del is predicted, which supports the idea of Alg8 being the polymerase responsible for alginate synthesis. (C) 1997 Elsevier Science B.V.