We used the interposon mutagenesis technique to map a cluster of Rhodobacter capsulatus genes that are responsible for the biosynthesis of carotenoids, membrane pigments that protect living organisms from photooxidations. Fifteen interposons define 7 genes (crtA, crtI, crtB, crtC, crtD, crtE and crtF) in an approximately 8 kb of the chromosome. This cluster is flanked by genes affecting bacteriochlorophyll biosynthesis. Based on the analysis of the phenotypes of the insertional mutants and the results of complementation analyses, we present a genetic and physical map of this region. Our data indicate that, with the possible exception of crtI and crtB, all genes analyzed are organized as single transcriptional units. We used nuclease S1 protection analysis to study the influence of oxygen on the regulation of expression of 4 genes (crtA, crtI, crtC and crtE). Under anaerobic conditions, mRNA levels for crtA, crtC and crtE are elevated and a new crtE transcript is detected. © 1988 Springer-Verlag.

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