The genome of the purple non-sulphur photosynthetic bacterium Rhodopse
udomonas acidophila has been found to contain multiple copies of puc l
ight-harvesting (LH2) peripheral. antenna complex genes. Three wild-ty
pe isolates each exhibiting dissimilar peripheral antenna complex phen
otypes in response to growth at reduced light intensity, were found to
contain different numbers of these genes. Twenty-three puc cross-hybr
idising clones were isolated from a genomic library constructed from R
hodopseudomonas acidophila strain 7050; two of which were examined fur
ther; 2.6kb from one clone was sequenced and found to contain three be
ta/alpha gene pairs designated puc(1)BA, puc(2)BA and puc(3)BA. The pu
tative translated polypeptides are very like, but not identical to tho
se from B800-820 complexes and upstream sequence homologies suggests t
hat this treble gene cluster has arisen through a relatively recent ge
ne duplication event. From the other clone 0.6kb was sequenced and fou
nd to contain a further gene pair, puc(4)BA, which is capable of encod
ing apoproteins for a B800-850-like complex. When the cells are grown
at 'high' or 'low' light intensity Northern analyses showed that only
puc(4)BA is expressed under 'high' light conditions. Furthermore, pucB
A mRNA transcripts were detected in all three species in the range 500
-780 nt. In Rhodopseudomonas acidophila post-transcriptional regulator
y mechanisms also play a role in determining the amount of peripheral
antenna present in the intra-cytoplasmic membrane.