Molecular analysis of the malR gene of Clostridium butyricum NCIMB 7423, a member of the LacI-GalR family of repressor proteins

Deletion of a region of DNA 5' to a previously characterised malQ gene of Clostridium butyricum resulted in increased production of the enzyme activity encoded by malQ, 4-alpha-glucanotransferase. Nucleotide sequence analysis revealed the presence of all open reading frame capable of encoding a protein of 335 amino acids. This protein was found to share 33% amino acid sequence identity with the Bacillus subtilis CcpA (catabolite control protein) repressor, 28% identity with the Streptomyces coelicolor MalR repressor, and 30%; 25%, and 21% amino acid identity with the Escherichia coli repressors GalR, LacI and MalI, respectively. The amino-terminal domain was predicted to be able to form a helix-turn-helix structure, and shared highest similarity with the equivalent functional domain from the E. coli LacI repressor. Interruption of malR by the generation of a frameshift mutation led to a 10-fold increase in MalQ activity. These data suggest that the identified open reading frame encodes a repressor of the C. butyricum malQ gene, and of the adjacent malP gene. The gene has, therefore, been designated malR, and its encoded gene product MalR. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.