Abstract
The avian leukosis virus subgroup K (ALV-K), a novel subgroup in Chinese indigenous chicken breeds, has been difficult to isolate in the past due to its poor replication ability. However, according to the latest monitoring data, the replication ability and isolation rate of ALV-K have clearly increased, and new strains with mutations in the pol gene have also been found. To determine the effects of such mutations on the biological characteristics of ALV-K, a pair of infectious clones were constructed and rescued. The first virus was an ALV-K Chinese isolate with mutations in its pol gene, named rSDAUAK-11. The second virus was a recuperative rSDAUAK-11 from which mutations in the pol gene were recovered according to the corresponding region of the ALV-K prototype virus JS11C1, named rRSDAUAK-11. In addition, two quantitative real-time polymerase chain reaction assays were developed to specifically detect these virus strains. Using such methods, we observed a marked improvement of the reverse transcriptase activity, replication ability and vertical transmission ability of rSDAUAK-11, which also revealed a formidable competitive advantage in mixed infection with rRSDAUAK-11 and corresponded to the differences between the wild strains SDAUAK-11 and JS11C1. Accordingly, our findings not only show that mutations in the pol gene are an important molecular mechanism contributing to corresponding changes in the biological characteristics of the newest ALV-K but also emphasize the potential future eradication of ALV.
Highlights
Avian leukosis is a vertically transmitted disease caused by the avian leukosis virus (ALV), which can cause serious immunosuppression, growth retardation and tumorinduced mortality
The mutations in the pol gene of the newly isolated avian leukosis virus subgroup K (ALV-K) To determine the molecular basis of the enhanced replication ability of the newly isolated ALV-K, the pol gene sequences of the SDAUAK-11 and corresponding reference strains from different subgroups were compared to observe the genetic differences among them
Mutations in the pol gene significantly enhanced reverse transcriptase activity and replication ability both in vitro and in vivo To assess the effects of such mutations on reverse transcriptase (RT) activity in vitro, commensurable SDAUAK-11, JS11C1, rSDAUAK-11 and rRSDAUAK-11 with the same virion number were evaluated for RT activity using a commercial kit
Summary
Avian leukosis is a vertically transmitted disease caused by the avian leukosis virus (ALV), which can cause serious immunosuppression, growth retardation and tumorinduced mortality. The results showed that the PVL of SDAUAK11 was significantly higher than that of JS11C1 at 2 or 3 HPI (P < 0.01), and similar results were obtained for the rescued viruses (Fig. 2d), which demonstrated that the enhanced RT activity resulting from mutations in the pol gene promoted the reverse transcription process of the novel ALV-K and accelerated its replication process.
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