Isolation and characterization of Marek's disease virus (MDV) cDNAs from a MDV-transformed lymphoblastoid cell line: identification of an open reading frame antisense to the MDV Eco-Q protein (Meq).

Two Marek's disease virus (MDV) cDNAs of 852 and 1168 bp, which map to the right end of the BamHI-I2 fragment of the MDV genome, were isolated from a cDNA library derived from the MDV transformed lymphoblastoid cell line MKT-1. These cDNAs hybridized to relatively abundant leftward mRNA transcripts in MKT-1 cells and cells lytically infected with MDV. The transcriptional initiation site for these transcripts was located in the adjacent BamHI-Q2 fragment, as determined by RNase protection and primer extension assays. A computer search for the presence of leftward open reading frames (ORFs) revealed two ORFs encoding 135- and 195-amino-acid polypeptides. A polyclonal antibody raised against a protein sequence in the N-terminus of the latter ORF detected a 23-kDa protein in the nuclear fraction of MDV-transformed lymphoblastoid cells. Furthermore, this ORF was antisense to part of the MDV Eco-Q protein (Meq) sequence.