POLY-BETA-HYDROXYBUTYRATE (PHB) BIOSYNTHETIC GENES IN RHIZOBIUM-MELILOTI-41

Genes encoding beta-ketothiolase (phaA), acetoacetyl-CoA reductase (ph aB) and PHB-synthase (phaC) from R. meliloti 41, together with a fourt h gene, referred to as ORF1, presumed to be involved in PHB biosynthes is, have been cloned and sequenced. phaA, phaB and ORF1 were identifie d by heterologous hybridization on a cosmid library, while phaC was is olated by cloning the transposon-tagged fragment from a R. meliloti PH B- Tn5 mutant. phaA and phaB were functionally expressed in Escherichi a coli while phaC was able to complement a PHB- strain of R. meliloti 41. The three genes were sufficient to direct the production of polyhy droxyalkanoate in E. coli. The homology of ORF1 with an ORF located ne ar the PHB genes in two phototrophic bacteria suggests its involvement in PHB synthesis.