Identification of a unique Marek's disease virus gene which encodes a 38-kilodalton phosphoprotein and is expressed in both lytically infected cells and latently infected lymphoblastoid tumor cells

Abstract

The identification of unique Marek's disease (MD) virus (MDV) antigens expressed not only in lytically infected cells but also in latently infected MD lymphoblastoid tumor cell lines is important in understanding the molecular mechanisms of latency and transformation by MDV, an oncogenic lymphotropic herpesvirus of chickens. Through cDNA and nucleotide sequence analysis, an open reading frame (designated the pp38 ORF) which encodes a predicted polypeptide of 290 amino acids was identified in BamHI-H. Demonstration that the pp38 ORF spans the junction of the MDV long unique and long internal repeat regions (MDV has an alphaherpesvirus genome structure) precludes the presence of the gene encoding the B-antigen complex (gplOO, gp6O, and gp49) in the same region of BamHI-H, where it was originally thought to exist. Duplication of the complete pp38 ORF was not observed in BamHI-D, but part of it (encoding 45 amino acids) was found in the long terminal repeat region of the fragment. By use of tipE-pp38 fusion proteins, antisera against pp38 were prepared. By immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a predominant virus-specific 38,000-dalton polypeptide (designated pp38) and a minor 24,000-dalton polypeptide (designated p24) were found. No precursor-product relationship was found between pp38 and p24 by pulse-chase analysis, and only pp38 was detected by Western blot (immunoblot) analysis with antiserum to pp38. pp38 was found to be phosphorylated and present in oncogenic serotype 1-but not nononcogenic serotype 3-infected cells. Expression of the gene encoding pp38 was relatively insensitive to phosphonoacetic-acid inhibition, suggesting that pp38 may belong to one of the early classes of herpesvirus proteins. pp38 was also detected in the latently infected MSB-1 lymphoblastoid tumor cell line. The detection of antibody against pp38 in immune chicken sera indicates that pp38 is an immunogen in birds with MD. Most of the properties described here for a protein detected by methods based on finding the ORF first are identical to those of a 38-kDa phosphoprotein reported by others, suggesting that they are the same. Collectively, the data reported here provide (i) more definitive information on the complete ORF of another MDV gene and the protein that it encodes, (ii) clarification of the gene content within a specific region of the MDV genome, and (iii) the molecular means to conduct further studies to determine whether pp38 plays a role in MDV latency and transformation.

Marek's disease virus latency-associated transcripts belong to a family of spliced RNAs that are antisense to the ICP4 homolog gene

“…4B). In contrast, the 1.8-kb MDV pp38 transcript (13,16) was found in the cytoplasmic RNA fraction, as expected (Fig. 4C).…”

Infectious Laryngotracheitis Herpesvirus Expresses a Related Pair of Unique Nuclear Proteins Which Are Encoded by Split Genes Located at the Right End of the ULGenome Region

“…The gene content of the U S genome regions in particular exhibits some variability between avian and mammalian alphaherpesviruses (7,62) and also between the more closely related human alphaherpesviruses (16). The tumorigenic MDV possesses a set of specific genes within the IR L and TR L sequences, including several putative oncogenes (5,13,33). Remarkably, the long repeat sequences of the MDV type E herpesvirus genome (12) positionally correspond to the ends of the U L region in the type D genomes of other alphaherpesviruses, including ILTV.…”

Retention of oncogenicity by a Marek's disease virus mutant lacking six unique short region genes

“…This region also contains the meq gene, which encodes a leucine-zipper-containing protein expressed in LBCLs (18). Genes encoding phosphoproteins pp38 and pp24 initiate in these repeats (2,9,20,46). These phosphoproteins are expressed in cells lytically infected with MDV serotype 1 strains as well as in LBCLs (9).…”

“…Genes encoding phosphoproteins pp38 and pp24 initiate in these repeats (2,9,20,46). These phosphoproteins are expressed in cells lytically infected with MDV serotype 1 strains as well as in LBCLs (9). cDNAs generated from transcripts expressed from these regions in LBCLs encode small open reading frames (15,30,31).…”