CLUSTERING AND COORDINATED ACTIVATION OF CAROTENOID GENES IN MYXOCOCCUS-XANTHUS BY BLUE-LIGHT

Blue light activates carotenoid production in the non-photosynthetic, Gram-negative bacterium Myxococcus xanthus. Light is known to stimulat e the expression of two unlinked genes for carotenoid synthesis, carB and carC, through a mechanism in which the regulatory genes carA, carQ and carR take part. Genes carQ and carR are linked together at a sepa rate locus, whereas carA is linked to carB. We have introduced Tn 5 at various sites between carA and carB. Chemical analyses of the mutant strains demonstrate the presence in this region of a cluster of genes for carotenoid synthesis. Gene expression analysis strongly argues for most (or all) of the genes in the cluster being transcribed from a si ngle, light-inducible promoter under the control of genes carA, carQ a nd carR.