A Cluster of Structural and Regulatory Genes for Light‐Induced Carotenogenesis in Myxococcus xanthus

Abstract

In the bacterium Myxococcus xanthus, several genes for carotenoid synthesis lie together at the carAcarB chromosomal locus and are co-ordinately activated by blue light. A 12-kb DNA stretch from wildtype M. xanthus has been sequenced that includes the entire carA-carB gene cluster. According to sequence analysis, the cluster contains 11 different genes. Intergenic distances are very short or nil (implying translational coupling), giving further support to previous evidence indicating that most (or all) of the genes in the cluster form a single operon. At the promoter region, a potential -35 site for the binding of ~7 factors is found. However, the -10 region shows little similarity with analogous sites in other bacterial promoters. Five (possibly six) genes in the curA-curB operon code for enzymes acting on early or late steps of the pathway for carotenoid synthesis. Other genes in the operon show no overall similarity with previously known genes. However, peptide stretches in the predicted products of two genes exhibit strong similarity with the DNA binding domain of the MerR family of transcriptional regulators. At least one of the predicted DNA-binding domains is altered in a mutant strain affected in light-regulation of the car genes.

A novel carotenoid 1,2-hydratase (CruF) from two species of the non-photosynthetic bacterium Deinococcus

“…Combining gene expression and disruption analysis, we confirmed that dr0091 and dgeo2309 encode a novel carotenoid 1,2-hydratase in D. radiodurans and D. geothermalis. The genes dr0091 and dgeo2309 showed little homology to the CrtC-type carotenoid 1,2-hydratase, which is found mainly in photosynthetic bacteria (Armstrong et al, 1989;Frigaard et al, 2004;Giraud et al, 2004;Kovács et al, 2003;Lang et al, 1995;Ouchane et al, 1997;Scolnik et al, 1980) and in the non-photosynthetic bacterium Myxococcus xanthus (Botella et al, 1995). Recently, a carotenoid 1,2-hydratase homologue of DR0091 and Dgeo2309 from the cyanobacterium Synechococcus sp.…”

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

“…One module, pI, is an 18-bp segment upstream of the promoter that displays dyad symmetry, with 6-bp repeats flanking a 6-bp intervening stretch. The design of this module resembles in some respects that reported previously for the operator of MerR, the prototypical member of a family of transcriptional regulators whose DNA binding domain shows sequence similarity to the N-terminal domain of CarA (16). In the absence of Hg(II), MerR represses expression of the mercury resistance operon merTP(C)AD but activates its expression when Hg(II) is present.…”

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

“…One corresponds to the single gene crtI and the other to an operon, carB, where the rest of the structural genes are grouped Botella et al, 1995). The precise mechanism for the light activation of the crtI promoter (P I ) differs from that of the carB promoter (P B ).…”