Multiple domain structure in a chitinase gene (chiC) of Streptomyces lividans

Abstract

One of the chitinases of Streptomyces lividans, chitinase C, was encoded by a 2 kb smaI-XhoI restriction fragment contained in the recombinant plasmid pEMJ7. DNA sequence analysis of this region revealed the presence of two open reading frames (ORF1 and ORF2) which had opposite orientations. Northern analysis showed that only the mRNA complementary to ORF1 was transcribed, and that this transcription was induced by chitin and repressed by glucose. ORF1 showed a codon distribution typical of Streptomyces. A sequence identical to that of the N-terminus of mature secreted chitinase C was found from amino acid residue 31 in the deduced amino acid sequence of ORF1 (619 amino acids), implying that ORF1 encodes a pre-protein of chitinase C. The pre-protein of chitinase C consisted of four discrete domains. The 30 amino acid N-terminal sequence, domain 1, was characteristic of a signal peptide. Domain 2 consisted of 105 N-terminal amino acids of mature chitinase C, and was similar to cellulose-binding domains of several cellulases. Domain 3 (94 amino acids) showed homology with type III homology units of fibronectin. Domain 4, a C-terminal 390 amino acid sequence, is probably the catalytic domain of the chitinase, since it exhibited identity with several other chitinolytic enzymes.