Abstract: Cryptochrome gene (Cry) is one of the major biological clock genes which were widely distributed in bacteria and eukaryotes. Cry genes of insect species are clearly divided into two types, Cry1 and Cry2. Only Cry1 is expressed in Drosophila, while only Cry2 was expressed in bees and other hymenopteran insects. In order to explore the molecular mechanism of circadian clock in lepidopteran model insect Bombyx mori and the evolution of CRY proteins in insect species, we cloned the cDNA sequences of Bmcry1 (2 166 bp, GenBank accession no. HM747059) and Bmcry2 (2 389 bp, GenBank accession no. HM747060), and obtained their gene sequences (GenBank accession no. HM747057 and HM747058, respectively) by sequence alignment and assembly. Bmcry1 have 12 exons and 11 introns, while Bmcry2 have 9 exons and 8 introns. Chromosome mapping showed that Bmcry1 and Bmcry2 were located on chromosome 17 and chromosome 15, respectively. We predicted the three-dimensional structures of Bmcry1 and Bmcry2 by homology modeling. The results showed that the FAD entrances are large and deep, consistent with the fact that CRY proteins do not bind with pyrimidine dimers, and the surfaces of Bmcry1 and Bmcry2 are more negatively charged, only FAD entrances have accumulated positive charge. Moreover, we researched the molecular evolution of Bmcry1 and Bmcry2 by multiple sequence alignment, protein motif analysis, functional domain analysis and cluster analysis. The results showed that Bmcry1 and Bmcry2 belonged to insect CRY1 and CRY2, respectively, and were closely to the corresponding proteins in other lepidopteran insects like Antheraea pernyi. Similar to the CRY proteins in other insects, Bmcry1 and Bmcry2 have DNA photolysis enzyme domain and FAD binding domain. However, the two domains have different conservative sites between CRY1 and CRY2 in insect species, and their protein motifs are also different. Our experiment provided a basis for further investigating the mechanism of molecular evolution and function of CRY1 and CRY2 in B. mori.

Key words: Bombyx mori, biological clock, cryptochrome gene, bioinformatic analysis, molecular evolution, homology modeling