Abstract: The Sip gene of the isolate M7 of Ⅰa serotype Streptococcus agalactiae from bovine was amplified using the PCR method,cloned into pGEM-T Easy vector and then sequenced. The molecular characteristics of Sip gene and its expression protein were analyzed using a variety of biological software. The results showed that Sip gene of M7 was 1305 bp and did not appear the gene deletion, the Sip gene of nucleotide sequence derived from M7 had a 98.0% to 100.0% of homology and a 97.2% to 99.8% amino acid homology among the corresponding sequences published in GenBank.Furthermore, the Sip gene of M7 shared of 100.0% nucleotide homology and 99.8% of amino acid identity with that of Ly2(FJ808732)strains in China and GB00549(FJ752159)in USA, respectively. The expression protein of Sip gene was a stable outer membrane protein,which was secretion protein and hydrophobic highly. The polypeptide contained a LysM functional domain which was related to immunoregulation between the N-terminal 52nd to 95th amino acid residues and a signal peptide consisting of 25 amino acids, which of cleavage site between 25th and 26th amino acids. Moreover there were a number of B cell and T cell epitopes on the protein. The results illustrated the Sip protein of M7 strain was conservative immune proteins without missing LysM superfamily domain.

Key words: bovine; Streptococcus agalactiae; surface immunogenic protein(Sip) gene; Ⅰa serotype