CLONING AND CHARACTERIZATION OF THE CHLOROPHYLL BIOSYNTHESIS GENE CHLM FROM SYNECHOCYSTIS PCC-6803 BY COMPLEMENTATION OF A BACTERIOCHLOROPHYLL BIOSYNTHESIS MUTANT OF RHODOBACTER-CAPSULATUS
Ca. Smith et al., CLONING AND CHARACTERIZATION OF THE CHLOROPHYLL BIOSYNTHESIS GENE CHLM FROM SYNECHOCYSTIS PCC-6803 BY COMPLEMENTATION OF A BACTERIOCHLOROPHYLL BIOSYNTHESIS MUTANT OF RHODOBACTER-CAPSULATUS, Plant molecular biology, 30(6), 1996, pp. 1307-1314
A bacteriochlorophyll a biosynthesis mutant of the purple photosynthet
ic bacterium Rhodobacter capsulatus was functionally complemented with
a cosmid genomic library from Synechocystis sp. PCC 6803. The complem
ented R. capsulatus strain contains a defined mutation in the bchM gen
e that codes for Mg-protoporphyrin IX methyltransferase, the enzyme wh
ich converts Mg-protoporphyrin IX to Mg-protoporphyrin IX methylester
using S-adenosyl-L-methionine as a cofactor. Since chlorophyll biosynt
hesis also requires the same methylation reaction, the Synechocystis g
enome should similarly code for a Mg-protoporphyrin IX methyltransfera
se. Sequence analysis of the complementing Synechocystis cosmid indica
tes that it contains an open reading frame exhibiting 29 % sequence id
entity to BchM. In addition, expression of the Synechocystis gene in t
he 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 represen
ts the first chlorophyll biosynthesis gene homolog of bchM. The comple
menting Synechocystis cosmid was also shown to code for a gene product
that. is a member of a highly conserved family of RNA binding protein
s, the function of which in cyanobacteria remains undetermined.