Poly $ = hydroxybutyrate ( PHB ) biosynthetic genes in Rhizobium meliloti 41

2 Dipartimento di Biotecnologie Agrarie, Universita di Padova, Via Gradenigo 6, 35131 Padova, Italy Genes encoding fiketothiolase (phaA), acetoacetyl-CoA reductase (phaB) and PHB-synthase (phaC) from R. meliloti 41, together with a fourth gene, referred to as ORF1, presumed to be involved in PHB biosynthesis, have been cloned and sequenced. phaA, phaB and ORFl were identified by heterologous hybridization on a cosmid library, while phaC was isolated by cloning the transposon-tagged fragment from a R. meliloti PHBTn5 mutant. phaA and phaB were functionally expressed in Escherichia coli while phaC was able to complement a PHBstrain of R. meliloti 41. The three genes were sufficient to direct the production of polyhydroxyalkanoate in E. coli. The homology of ORFl with an ORF located near the PHB genes in two phototrophic bacteria suggests its involvement in PHB synthesis.