THE PURPLE PHOTOSYNTHETIC BACTERIUM RHODOPSEUDOMONAS-ACIDOPHILA CONTAINS MULTIPLE PUC PERIPHERAL ANTENNA COMPLEX (LH2) GENES - CLONING AND INITIAL CHARACTERIZATION OF 4 BETA ALPHA PAIRS/

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.