Study on the structure of heteropolymer pp38/pp24 and its enhancement on the bi-directional promoter upstream of pp38 gene in Marek's disease virus.

In the latest report, Chloramphenicol acetyltransferase (CAT) gene was used as a reporter to investigate the influence of pp38 on its upstream bi-directional promoter, and it was found that the co-expression of pp38 and pp24 can significantly enhance the transactivity of the bi-directional promoter between pp38 gene and 1.8-kb mRNA transcript in genome of Marek's disease virus (MDV). In this study, enhanced green fluorescence protein (EGFP) gene was used as another reporter to further investigate the promoter activity. The transfection shows the promoter has the complete activity under the condition of co-expression of pp38 and pp24 in the same cells. Immunoprecipitation test was used to verify the structure of pp38/pp24 heteropolymer. The pp38-specific monoclonal antibody H19 was used in this test, and pp38, pp24 or both were prepared from the pcDNA-pp38, pcDNA-pp24 or pBud-pp38-pp24 transfected chicken embryonic fibroblast (CEF), respectively. Immunoprecipitation indicates that pp24 could be co-precipitated with pp38 by MabH19, implying that pp24 and pp38 were able to form a heteropolymer in the natural condition. The two separated tests clarify that pp38 and pp24 form a heteropolymer, which enhances the activity of the promoter.