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Chitin is the most widespread amino polysaccharide in nature.Chitin synthase (CHS) plays an important role in chitin formation in the cuticle and the peritrophic membrane (PM) lining the midgut.Total RNA was isolated from the cuticle of Mamestra brassicae (L.) fourth instar larva.cDNA sequence was cloned by RT-PCR and Rapid Amplification of cDNA Ends (RACE).cDNA,5 220 bp in length,contained an open reading frame of 4 704 bp coding for a polypeptide of 1 567 amino acid residues with a predicted molecular weight of 178.3 ku and its pi was 6.42.The deduced amino acid sequence from M.brassicae (L.) shared the high level of identity with chitin synthase sequences from other insects,especially lepidopteran insects.cDNA sequence has been deposited with GenBank under accession No.GQ281761.