A CLUSTER OF STRUCTURAL AND REGULATORY GENES FOR LIGHT-INDUCED CAROTENOGENESIS IN MYXOCOCCUS-XANTHUS

In the bacterium Myxococcus xanthus, several genes for carotenoid synt hesis lie together at the carA-carB chromosomal locus and are co-ordin ately activated by blue light. A 12-kb DNA stretch from wildtype M. xa nthus has been sequenced that includes the entire carA-carB gene clust er. According to sequence analysis, the cluster contains 11 different genes. Intergenic distances are very short or nil (implying translatio nal coupling), giving further support to previous evidence indicating that most (or all) of the genes in the cluster form a single operon. A t the promoter region, a potential -35 site for the binding of sigma f actors is found. However, the -10 region shows little similarity with analogous sites in other bacterial promoters. Five (possibly six) gene s in the carA-carB operon code for enzymes acting on early or late ste ps of the pathway for carotenoid synthesis. Other genes in the operon show no overall similarity with previously known genes. However, pepti de stretches in the predicted products of two genes exhibit strong sim ilarity with the DNA binding domain of the MerR family of transcriptio nal regulators. At least one of the predicted DNA-binding domains is a ltered in a mutant strain affected in light-regulation of the car gene s.