Cloning and characterization of the chlorophyll biosynthesis gene chlM from Synechocystis PCC 6803 by complementation of a bacteriochlorophyll biosynthesis mutant of Rhodobacter capsulatus.
A bacteriochlorophyll a biosynthesis mutant of the purple photosynthetic bacterium Rhodobacter capsulatus was functionally complemented with a cosmid genomic library from Synechocystis sp. PCC 6803. The complemented R. capsulatus strain contains a defined mutation in the bchM gene that codes for Mg-protoporphyrin IX methyltransferase, the enzyme which converts Mg-protoporphyrin IX to Mg-protoporphyrin IX methylester using S-adenosyl-L-methionine as a cofactor. Since chlorophyll biosynthesis also requires the same methylation reaction, the Synechocystis genome should similarly code for a Mg-protoporphyrin IX methyltransferase. Sequence analysis of the complementing Synechocystis cosmid indicates that it contains an open reading frame exhibiting 29% sequence identity to BchM. In addition, expression of the Synechocystis gene in the R. capsulatus bchM mutant via the strong R. capsulatus puc promoter was shown to support nearly wild-type levels of bacteriochlorophyll a synthesis. To our knowledge, the Synechocystis sequence thus represents the first chlorophyll biosynthesis gene homolog of bchM. The complementing Synechocystis cosmid was also shown to code for a gene product that is a member of a highly conserved family of RNA binding proteins, the function of which in cyanobacteria remains undetermined.
Smith
C A
CA
Department of Biology, Indiana University, Bloomington 47405, USA.
Suzuki
J Y
JY
Bauer
C E
CE
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001429:Bacteriochlorophylls / Q000096:biosynthesis*; D001483:Base Sequence; D002734:Chlorophyll / Q000096:biosynthesis*; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000235:genetics*; D005816:Genetic Complementation Test; D008780:Methyltransferases / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D016354:Rhodobacter capsulatus / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D002734:Chlorophyll; D008780:Methyltransferases; C100792:chlM protein, Synechocystis sp.; C060234:magnesium-protoporphyrin methyltransferase