LysR-type transcriptional regulator ChiR is essential for production of all chitinases and a chitin-binding protein, CBP21, in Serratia marcescens 2170

To identify the genes required for chitinase production by Serratia marcesc ens 2170, various Tn5 mutants somehow defective in chitinase production wer e isolated in a previous study. In order to identify the mutated gene in on e of the chitinase-deficient mutants, N1, DNA regions flanking the Tn5 inse rtion were cloned and sequenced. Sequence comparison showed that the mutati on occurred in the ORF located between chiB and cbp, which encode chitinase B and chitin-binding protein CBP21, respectively. The ORF encodes a 313-am ino acid polypeptide which has significant similarity with various LysR-typ e transcriptional regulators, and thus the gene was designated chiR. Target ed mutagenesis confirmed that disruption of the chiR gene results in the ph enotype of N1. Gel mobility shift assays using partially purified ChiR prot ein demonstrated that this protein specifically binds to the intergenic reg ion between chiR and cbp. These results strongly suggest that ChiR is a Lys R-type transcriptional regulator which is essential for production of all c hitinases and CBP21.