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Vitamin B 12 partners the CarH repressor to downregulate a photoinducible promoter in Myxococcus xanthus
Author(s) -
PérezMarín Mari Cruz,
Padmanabhan S.,
Polanco María Carmen,
Murillo Francisco José,
ElíasArnanz Montserrat
Publication year - 2008
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2007.06086.x
Subject(s) - myxococcus xanthus , operon , biology , repressor , psychological repression , lac operon , operator (biology) , gene , promoter , lac repressor , genetics , transcription factor , microbiology and biotechnology , gene expression , escherichia coli , mutant
Summary A light‐inducible promoter, P B , drives expression of the carB operon in Myxococcus xanthus . Repressed by CarA in the dark, P B is activated when CarS, produced in the light, sequesters CarA to prevent operator‐CarA binding. The MerR‐type, N‐terminal domain of CarA, which mediates interactions with both operator and CarS, is linked to a C‐terminal oligomerization module with a predicted cobalamin‐binding motif. Here, we show that although CarA does bind vitamin B 12 , mutating the motif involved has no effect on its ability to repress P B . Intriguingly, P B could be repressed in the dark even with no CarA, so long as B 12 and an intact CarA operator were present. We have discovered that this effect of B 12 depends on the gene immediately downstream of carA . Its product, CarH, also consists of a MerR‐type, N‐terminal domain that specifically recognizes the CarA operator and CarS, linked to a predicted B 12 ‐binding C‐terminal oligomerization module. The B 12 ‐mediated repression of P B in the dark is relieved by deleting carH , by mutating the DNA‐ or B 12 ‐binding residues of CarH, or by illumination. Our findings unveil parallel regulatory circuits that control a light‐inducible promoter using a transcriptional factor repertoire that includes a paralogous gene pair and vitamin B 12 .