title: Isolation and characterization of enhanced fluorescence mutants of Rhodopseudomonas capsulata.
abstract: After enrichment by a tetracycline suicide under conditions nonpermissive for the growth of mutants defective in photosynthesis, colonies were screened for enhanced fluorescence in near-infrared light by using high-speed infrared photography. Twenty mutants were isolated, and the chromatophore membranes were analyzed by a new, rapid microprocedure that revealed many different phenotypes among the mutants. The enhanced fluorescence mutants typically possessed a functional light-harvesting II antenna, but showed reduced or absent light-harvesting I. Twelve isolates were also defective in reaction center polypeptides. An R-prime plasmid that bears 50 kilobases of Rhodopseudomonas capsulata DNA coding for components of the photosynthetic apparatus (B. L. Marrs, J. Bacteriol. 146:1003-1012, 1981), pRPS404, complemented all 20 enhanced fluorescence mutants as demonstrated by the quenching of fluorescence in mutants that had received the R-prime plasmid by conjugation. Fluorescence was regained upon loss of the 50-kilobase insert. Complementation of the fluorescent lesions implies that most or all of the genes necessary for the expression of the reaction center and the light-harvesting antennae are carried by the R-prime plasmid and that these genes are actively transcribed in the homologous organism. All 20 mutants are complemented by one of two pBR322 subclones of the R-prime plasmid, pRPSEB2 or pRPSE2. pRPSEB2 bears a 4.5-kilobase fragment of R. capsulata DNA including the rxcA locus, and pRPSE2 is a pBR322 derivative bearing a 7.5-kilobase R. capsulata DNA fragment bearing the rxcB locus. These fragments therefore carry sequences necessary for the normal synthesis of the light-harvesting and reaction center polypeptide complexes.
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D005453:Fluorescence; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D005819:Genetic Markers; D009154:Mutation; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D011815:R Factors; D012241:Rhodopseudomonas / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D005819:Genetic Markers; D045322:Photosynthetic Reaction Center Complex Proteins