| Chymotrypsin inhibitor(CI) in Bombyxmon play an important role in the normal development and growth. So far researchers have done a relatively detailed study in its genetic rule, mapping in chromosome, purification, primary property of proteins, genomic sequence and gene structure, profile and regulation of expression, physiological role and so on. In the present research, the distribution of CI polymorphism was first investigated. Then a new CI gene was cloned and analysized. At last, analysis of all genes of CI was carried out based on the whole genome sequence of silkworm.Investigation of the distribution of CI polymorphism was carried out by native-polyacrylamide gel electrophoresis(Native-PAGE) in 425 silkworm strains using hemolymph as material. Results showed that three genes, Ict-E, Ict-D and Ict-A, express in every strain, and there is no expression of both genes Iet-Hand Ict-B in 16 strains. This result indicates that Ict-E, Ict-D and Ict-A are probably necessary for normal development of silkworm and genes Ict-H and Ict-B seems not necessary since lost expression of them only cause slow development, no significent deficiency showed. Also, results showed that the distribution of CI is coincident between Chineses and Japanese strains. Finally CI-5, CI-11 and CI-12 express in several strains. CI-5 experess together with CI-6, and CI-11 and CI-12 with. CI-13. Similar character of their expression profile suggests that CI-11 and CI-12 should be assign as CI-13'a and CI-13'b if CI-13a and CI-13b existed in silkworm. Cluster analysis was done with the result of investigation 52 pure strains by the software DPS. The result showed that the clustered group is not related to the tivoltine, moltinism, system or other biologic charater. Therefore existing of CI genes wildly in different strains suggest they may involve in fundamental biochemistry and physiology of silkworm.A new CI gene was amplified from the genome and cDNA of strain 13-121 with the specific primer designed by mRNA of SCI-SB. The analysis of its structure showed that it contains three exons. No retroposon-like DNA element Bm1 presents in introns. Border of intron and exton sequences confirmed the GT-AG rule. Comparatively, this structure is similar to the one of Cl-b1 and CI-13. The compelete ORF of 255 bp was cloned. It is predicted coding a putative precursor of 85 aa, of which the first 23 aa is the signal peptides. MW and pI of the putative mature protein was predicted to be 7059.81 Da and 4.49. A Kunitz domain was also found in it. Compare to the known CIs, there is five conserved cys residues in the predicted protein and the active site is as the same as the ones of CIs coded by gene Ict-A. Homolog search in genebank found the new gene is homolog with the CIs of silkworm. All of this suggests the new gene should be a Kunitz CI gene. So the new gene was assigned as CI-X. By RT-PCR analysis, expression of CI-X was detected in six tissues of...
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