The Influence Of 5′-untranslated Region On The Biological Characteristics Of CSFV C-strain

Classical Swine Fever(CSF) caused by Classical Swine Fever Virus(CSFV) is a highly contagious and hemorrhagic disease of pigs and is classified as a notifiable animal disease by Office International des Epizooties(OIE). Outbreaks of CSF usually lead to significantly economic losses in many countries worldwide. In China CSF was classified in the first class animal diseases and was broght into the program of compelling immunization.Hog Cholera Lapinized Virus(HCLV or C-strain) produced in our country is a attenuated strain from virulent strain in rabbit and shows poor growth in cells culture as the titer is very low, but it can cause a typical fever reaction in rabbit. Thiverval strain(T strain) is a temperature-sensitive mutant strain from Alfort strain and appeares good growth in cells culture without fever reaction in rabbit.5′-untranslated region(5′-UTR) of CSFV genome control the protein translation of the virus. CSFV 5′-UTR has Internal Ribosome Enty Site(IRES) which induce the initiation translation insteated of the cap-depented mechanism. The changes of the stucture and function of IRES indrectly influence the efficiency of translation initiation. It is reporeted that virulence strains of CSFV expressed higher ability of combine with cells and releasing virus than the middle and low virulence strain in cell culture. What confered that the discrepancy in primary and secondary structure of 5′-UTR may be a cause of that CSFV C-strain and T-strain have different cell culture characters.In the study, we analyzed the primary and second structrue of CSFV C-strain, Thiverval-strain and Shimen-strain by biology software. The results of primary structure showed that there had 13 bases differ. The secondy structure showed that there was no difference in number and stucture of hairpins in domain II and domain III between CSFV T-strain and Shimen-strain, but have significant difference with CSFV C-strain. But it had been proved that domain II and domain III of CSFV 5′-UTR have influence in the function of IRES. The secondery structure analysis also showed that the free energy of CSFV C-strain is higher than that of CSFV T-strain and Shimen., and ascending of the free energy aggravated unstable of the secondary structure influence the RNAsynthey possibly.For reaserch the interaction of the structure of 5′-UTR with the cell culture and virus titer of CSFV C-strain, two full-length genomic cDNA clone p T5′-UTR-C and p C5′-UTR –T has been constructed through the recombinant ligations in vitro, which on the basis of the analysis of the whole genome sequence of CSFV C-strain. Then v T5′-UTR –C and vC5′UTR –T were rescued by electrotransfected into cells. The cell culture showed that vT5’-UTR-C had a higher titer than CSFV C-strain.For reaserch the relationship between the 5’-UTR of the CSFV C-strain and fever reaction of rabbits, the two new virus were challeged to rabbits and tempreture of rabbits were recorded. The resultshowed that vT5′-UTR –C can reduce fever reaction of rabbits as the CSFV C-strain did. And v C5′-UTR –T showed the same character with CSFV T-stain. It indicated that the 5’-UTR has no relation with CSFV C-strain’s character that induce fever reaction of rabbits. Then the two new virus were challeged pigs. The pigs were all in health.In summary, 5’UTR has a certain extent influence in cell culture of CSFV C-strain but is not the only element.