During this decade, there have been major advancements in the understa
nding of genetic loci involved in synthesis of the family of Mg-tetrap
yrroles known as chlorophylls and bacteriochlorophylls. Molecular gene
tic analysis of Mg-tetrapyrrole biosynthesis was initiated by the perf
ormance of detailed sequence and mutational analysis of the photosynth
esis gene cluster from Rhodobacter capsulatus. These studies provided
the first detailed understanding of genes involved in bacteriochloroph
yll a biosynthesis. In the short time since these studies were initiat
ed, most of the chlorophyll biosynthesis genes have been identified by
virtue of their ability to complement bacteriochlorophyll a biosynthe
sis mutants as well as by sequence homology comparisons. This review i
s centered on a discussion of our current understanding of bacterial,
algal, and plant genes that code for enzymes in the Mg-branch of the t
etrapyrrole biosynthetic pathway that are responsible for synthesis of
chlorophylls and bacteriochlorophylls.