The purple photosynthetic bacterium Rhodopseudomonas acidophila contains multiple puc peripheral antenna complex (LH2) genes: Cloning and initial characterisation of four ?/? pairs

Abstract

The genome of the purple non-sulphur photosynthetic bacterium Rhodopseudomonas acidophila has been found to contain multiple copies of puc light-harvesting (LH2) peripheral antenna complex genes. Three wild-type isolates each exhibiting dissimilar peripheral antenna complex phenotypes in response to growth at reduced light intensity, were found to contain different numbers of these genes. Twenty-three puc cross-hybridising clones were isolated from a genomic library constructed from Rhodopseudomonas acidophila strain 7050; two of which were examined further; 2.6kb from one clone was sequenced and found to contain three β/α gene pairs designated puc (1)BA, puc (2)BA and puc (3)BA. The putative translated polypeptides are very like, but not identical to those from B800-820 complexes and upstream sequence homologies suggests that this treble gene cluster has arisen through a relatively recent gene duplication event. From the other clone 0.6kb was sequenced and found to contain a further gene pair, puc (4)BA, which is capable of encoding 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, pucBA mRNA transcripts were detected in all three species in the range 500-780 nt. In Rhodopseudomonas acidophila post-transcriptional regulatory mechanisms also play a role in determining the amount of peripheral antenna present in the intra-cytoplasmic membrane.