Cloning Of S Gene Of Infectious Bronchitis Virus And Its Expression In Prokaryocyte

Infectious bronchitis virus (IBV) causes a highly contagious disease in chickens. Various IBV isolates have been identified at the different regions of the world. Although live attenuated vaccines were available, infectious bronchitis continues to cause considerable economic losses in chicken industry because of the appearance of new IBV serotypes.Jiyong Zhou et.al.(1997) isolated an IBV strain named IBV-ZJ971 from swollen proventiculus hi sick chickens. The homology of SI gene of IBV-ZJ971 and HI20 is very high (99.4%) while the tropism of the two strains is quite different To further understand the molecular characteristics of variant IBV strain ZJ971, the S gene of ZJ971 was cloned, sequenced and analysed, and was then expressed hi prokaryocyte. These works lay a basic foundation of developing molecularly engineered vaccine against IBVCompared with other IBV strains, high homologies are shown between ZJ971 S gene and IBV strain H52, M41, KB8523 and Beaudette. However, the highest homology was found to be 99.71% between ZJ971 and H52. Several point mutations of the nucleotides appear at position 343rd, 395th, 484th, 2555th, 2706th and 3241st. Most important mutation is G to T point mutation at 3241st, which is responsible in forming a stop code of S gene of IBV strain ZJ971 that resulted into termination of translation of S protein ahead. And therefore, leading to a short of 82 amino acid, when compared with other IBV reference strains. The deduced primary structure of S protein of ZJ971 reveals that point mutation of amino acids appeared at residues 115th, 130th, 132nd,162nd and 852nd. These mutions cuase hydrophobic and hydrophilic changes of S protein, notably, the mutation at position 130th and 132nd from arginine or other amino acids to proline resulting into loss of a helix in secondary structure of IBV-ZJ971 strain S protein. These mutational characteristics show that IBV strain ZJ971 is a novel variant IBV.The S protein of ZJ971 was inserted into pBV220 and expressed completely in E.coli.DH5a. This result indicates that large S protein can be expressed in prokaryocyte to carry out further studies of the structure proteins of IBV and new vaccine against IBV.