IDENTIFICATION OF AN IMMEDIATE-EARLY GENE IN THE MAREKS-DISEASE VIRUSLONG INTERNAL REPEAT REGION WHICH ENCODES A UNIQUE 14-KILODALTON POLYPEPTIDE

Marek's disease virus (MDV) is an oncogenic avian herpesvirus at hose genomic structure is similar to those of herpes simplex virus and vari cella-zoster virus. Repeat regions of the MDV genome have been intensi vely investigated because of a potential relationship to MDV oncogenic ity and abundant expression of immediate-early transcripts. In this st udy, a 1.6-kb immediate-early transcript was localized to the BamHI-I- 2 region by Northern (RNA) hybridization analysis. With cDNA cloning a nd sequencing, two cDNAs of 1.4kb (C1) and 1.35 kb (C2) were identifie d. Both cDNAs are derived from spliced mRNAs spanning the BamHI-H and -I-2 fragments. C1 and C2 use the same splice acceptors and 3' ends, b ut they differ at their 5' ends and utilize different splice donors. T he upstream promoter-enhancer region of C1 cDNA has been defined as a bidirectional regulatory region shared by the MDV pp38 gene. Sequencin g analysis shows two small open reading frames (ORFs) within each cDNA (ORF1a and ORF2 in C1, ORF1b and ORF2 in C2). Potential ORFs of the s equence have no significant homology with any known protein in the Swi ss-Protein data base. DNA fragments encoding ORF1a and ORF1b were clon ed into pGEX-3X vectors to produce glutathione S-transferase fusion pr oteins and induce antisera. In Western blot (immunoblot) analysis of M DV-infected-cell lysates, a 14-kDa polypeptide was identified by antis era against both ORF1a and ORF1b. This 14-kDa protein is expressed in cells which are lytically infected with MDV strains GA, Md11 passage 1 4 (oncogenic), and Md11 passage 83 (attenuated), as well as in the lat ently MDV-infected and transformed MSB-1 cell line.