Cloned fragments of the region of the Rhodopseudomonas capsulata chromosome coding for components of the photosynthetic apparatus will be used to study transcriptional events associated with membrane differentiation in this bacterium. These fragments will also be used to test cryptic plasmids found in R. capsulata to see whether they carry the genes for photosynthesis. Transcriptional events will be examined by RNA-DNA hybridization following induction of photosynthetic membrane formation by decreasing O2 tension.