The nonessential UL49.5 gene of infectious laryngotracheitis virus encodes an O-glycosylated protein which forms a complex with the non-glycosylated UL10 gene product

The UL10 and UL49.5 genes of avian infectious laryngotracheitis virus (ILTV) encode putative envelope proteins which are conserved in Alpha, Beta, and Gammaherpesvirinae. Many of the corresponding gene products have been shown to be glycosylated and to form heterodimeric protein complexes with each other. Unlike the homologous gM proteins of other herpesviruses, the UL10 protein of ILTV is not detectably glycosylated [Fuchs, W., Mettenleiter, T.C., 1999. DNA sequence of the UL6 to UL20 genes of infectious laryngotracheitis virus and characterization of the UL10 gene product as a nonglycosylated and nonessential virion protein. J. Gen. Virol. 80, 2173–2182]. Using a monospecific antiserum, we now identified the UL49.5 gene product of ILTV as an O-glycosylated membrane protein (gN). Correct processing of gN was shown to depend on the presence of the UL10 protein. Both gN and UL10 could be co-immunoprecipitated from ILTV-infected cell lysates with antisera against either of the proteins, indicating stable protein–protein interactions. For functional analysis parts of the UL10 and UL49.5 open reading frames were deleted from the ILTV genome, and replaced by a β-galactosidase expression cassette. The resulting virus mutants were isolated and propagated in non-complementing chicken cells, which demonstrated that the UL10 and UL49.5 genes are not essential for in vitro replication of ILTV.