PHYLOGENETIC RELATIONSHIP OF PORCINE ENDOGENOUS RETROVIRUS (PERV) IN CHINESE PIGS WITH OTHER PATHOGENIC TYPE C RETROVIRUSES

O470 Aims: To predict the possible pathogenesis of PERV by analyzing the relationship between PERV and other pathogenic retrovirus. Methods: The approximately 189-bp (gag) and 212-bp (pol) PCR products were extracted and cloned into the pGEM-T vector (Promega). The analysis of all sequences was done by the ClustalX software. To estimate the level of divergence between PERV in Chinese pigs and other retroviruses, pol amino acid sequence of PERV was compared with that of other various type C and lentivirus, consisting of Baboon endogenous retrovirus (BaEV), simian sarcoma virus (SMSAV), Koala endogenous retrovirus (KoEV) and gibbon ape leukemia virus (GALV) (nonhuman primates), murine leukemia virus (MuLV), murine endogenous retrovirus (MuEV), murine AIDS virus related provirus (MAIDSV), feline leukemia virus (FeLV), fowlpox virus (FoPV); human immunodeficiency virus I (HIV-1), human endogenous retrovirus (HERV), spleen necrosis virus (SPNV) and spleen focus-forming virus (SFFV). A neighbor-joining phylogenetic tree was constructed from translated amino-acid sequences by the use of phylip95 software. Results: 1.The pol products were related to gamma-retroviruses. The pol sequences of three strains of Chinese pigs and other retroviruses differed in the reverse transcriptase region, which specified the specificity of activity. The amino acid identity showed that there existed two highly conserved sequences in PERV and other mammalian retrovirus (eleven and twenty-three amino acid residues, respectively). A nearly perfect match (20 of 22) of these amino acids to the murine, feline and gibbon ape leukemia viruses was found in the sequences encoded by PERV of the three strains of tested Chinese pigs. 2. Gag protein from Chinese pigs was analysed and gag phylogenetic trees with several clusters of type C retrovirus were constructed. In the first cluster, PERV-BMI and MuLV were closely related to each other, the other two PERV subgroups PERV-B and PERV-MSL, as well as FeLV and BaEV, were also found in this cluster. Comparing BMI-PERV-gag with other reported PERV sequences, we found that there was 16 amino sites were different and one lost between PERV-BMI and PERV-B, PERV-MSL. This observation indicated that the gag sequence from Chinese BMI belongs to a novel group related to several other type C retroviruses such as MuLV, FeLV and BaEV. Compared with other type C retrovirus such as SMSAV, SFFV and KoEV, the protein genetic phylogenetic distance gap was too large. Conclusions: All analyzed sequences showed two super-conserved motifs. The one His-Ser-Phe-Leu-Val-X-Cys-Pro-X-Pro-Leu-Leu-Gln-X-Leu-X-Lys belonged to reverse transcriptase (RT), which might suggest that PERVs and other gamma-retrovirus share the similar RT ability in the process of infecting host cells. Another one Arg-Gln-X-Lys-Asn-Leu-Thr-X-Ile-Leu-Ala-Ala-Val-Val between PERV-BMI and other type C retrovirus was a type C specific motif. PERVs, either from these three strains of Chinese pigs or other countries’ pigs, were closely related to other type C retrovirus and leitivirus, such as MuLV, BaEV, GALV, HERV, HIV and FeLV analyzed in this paper. However, based on reported results, PERV seemed not to cause transmitted disease. Ericsson found that the PERV clones were highly mutated and defective. The concern that human retroviral sequences would rescue the defective porcine endogenous retrovirus and then generate a pathogenic retrovirus seemed impossible.