A novel regulatory gene for light‐induced carotenoid synthesis in the bacteriumMyxococcus xanthus

Abstract

SummaryMyxococcus xanthus cells respond to blue light by producing carotenoids. Light triggers a network of regulatory actions that lead to the transcriptional activation of the carotenoid genes. By screening the colour phenotype of a collection of Tn 5-lac insertion mutants, we have isolated a new mutant devoid of carotenoid synthesis. We map the transposon insertion, which co-segregates with the mutant phenotype, to a previously unknown gene designated here as carF . An in frame deletion within carF causes the same phenotype as the Tn 5 -lac insertion. The carF deletion prevents the activation of the normally lightinducible genes, without affecting the expression of any of the regulatory genes known to be expressed in a light-independent manner. Until now, the switch that sets off the regulatory cascade had been identified with light-driven inactivation of protein CarR, an antisigma factor. The exact mechanism of this inactivation has remained elusive. We show by epistatic analysis that the carF gene product participates in the light-dependent inactivation of CarR. The predicted CarF amino acid sequence reveals no known prokaryotic homologues. On the other hand, CarF is remarkably similar to Kua, a family of proteins of unknown function that is widely distributed among eukaryotes.

An anti-antisigma factor in the response of the bacterium Myxococcus xanthus to blue light

“…Strong genetic evidence indicates that CarF is the earliest acting of all known Car elements of the light-driven regulatory cascade, being absolutely necessary for the lightdependent inactivation of CarR (Fontes et al, 2003). Contrary to all other known Car regulatory proteins, CarF does not take part in the carotenogenic response to copper (Moraleda-Muñoz et al, 2005).…”

The CarA/LitR-Family Transcriptional Regulator: Its Possible Role as a Photosensor and Wide Distribution in Non-Phototrophic Bacteria

“…The complex regulatory network retained by this unique bacterium involves multiple transcriptional regulators and associated proteins. 1,2) Recently, we found that Streptomyces coelicolor A3(2), a Gram-positive soil bacterium, produces carotenoid when exposed to light. 3) Evidence showed that LitR, a MerR-family protein, serves as a photo-dependent transcriptional regulator for litS, which encodes an ECF family sigma factor that specifies the transcription of carotenoid biosynthesis genes (crt).…”

“…The cloned DNA fragment contained the litQRS cluster and a flanking promoter region, PcrtY. PcrtY is a LitSdependent promoter that directs the transcription of one of the two operons for carotenoid biosynthesis, crtYTU, in S. coelicolor A3 (2). By the plasmid construction, PcrtY directed the transcription of a promoter-less mel operon that was located downstream from the promoter in the same orientation.…”

Operator Design and Mechanism for CarA Repressor-mediated Down-regulation of the Photoinducible carB Operon in Myxococcus xanthus

“…Six of these enzymes are encoded by this operon and only one by crtI (14 -16). carF is a recently identified gene whose product has been proposed to function as an anti-anti-factor at the earliest step in the regulatory cascade (17). The carQRS locus is a key regulatory operon that encodes three proteins with low, basal levels of expression in the dark: the extracytoplasmic function -factor CarQ (18 -20), its antifactor CarR (18,20), and the antirepressor protein CarS (21,22).…”

“…The carQRS locus is a key regulatory operon that encodes three proteins with low, basal levels of expression in the dark: the extracytoplasmic function -factor CarQ (18 -20), its antifactor CarR (18,20), and the antirepressor protein CarS (21,22). Central to the induction of carotenogenesis on exposure to light is the CarF-mediated inactivation of CarR to release CarQ (17,18). Once liberated, CarQ up-regulates expression of car-QRS and crtI (18).…”