Cloning of a new antenna gene cluster and expression analysis of the antenna gene family of Rhodopseudomonas palustris

The genome of Rhodopseudomonas palustris contains five antenna gene clusters, αβa, αβb, αβc, αβd and αβe, which encode the light-harvesting peripheral antenna complex II polypeptides. The isolation and characterisation of the gene which encodes the αe and βe polypeptides are reported. The primary structure of the βe polypeptide is identical to that of βb whilst the structure of αe is different from the other α subunits so far characterised. All five of the gene clusters were transcribed under high-light conditions while under low-light conditions only three were transcribed (αβb, αβd and αβe). Furthermore, Northern-blot analysis showed that the gene clusters encode RNA transcripts of either 500 or 650 nucleotides. Individual members of the gene family showed a differential response in terms of the regulation of abundance of mRNA upon growth under either high-light or low-light intensities. Possible promoter sequences and operator sites upstream of the αβb, αβd and αβe genes were located. Furthermore using puc-lacZ fusions in trans in R. palustris, we were able to examine the positions of the promoter of the gene clusters. The significance of these observations with respect to the regulation, organization and role of the peripheral antenna is discussed.