Mutations in catabolite control protein CcpA separating growth effects from catabolite repression

Abstract

Carbon catabolite repression in Bacillus megaterium is mediated by the transcriptional regulator CcpA. A chromosomal deletion of ccpA eliminates catabolite repression and reduces the growth rate on glucose. We describe four single-amino-acid mutations in CcpA which separate the growth effect from catabolite repression, suggesting distinct regulatory pathways for these phenotypes.

FIG. 1

Growth of selected mutants on solid and liquid minimal media with 0.5% glucose as the sole source of carbon. To score growth on solid medium, cells were streaked on plates and incubated at 30°C for 20 h. Single colonies were excised with the surrounding agar and resuspended in liquid medium. The number of CFU was determined by plating aliquots from serial dilutions (hatched bars). Growth rates in liquid medium were determined at 32°C with vigorous agitation (open bars).

FIG. 2

Sequence alignment of the N termini of B. megaterium (Bme) and B. subtilis (Bsu) CcpA and the purine and lactose repressors of E. coli (Eco). Identical amino acids are shaded. Numbered boxes below the sequences denote α-helices, as determined for PurR. The positions of amino acid exchanges of mutants isolated in this study are given above the sequences.