MOLECULAR ANALYSIS OF THE GLYCOPROTEIN C-NEGATIVE PHENOTYPE OF ATTENUATED MAREKS-DISEASE VIRUS

Serial passage of oncogenic serotype 1 Marek's Disease virus (MDV) in cultured avian cells results in attenuation of viral oncogenicity and pathogenicity. Coincident with attenuation, expression of MDV glycopro tein C (gC) is significantly reduced. Regulation of MDV gC may have im portant implications for virus-host interactions and have important co nsequences in the process of viral attenuation. To investigate the mec hanism by which MDV gC expression is reduced during attenuation of the very virulent serotype 1 MDV strain Md11, protein levels, gene struct ure, steady-state RNA levels, and transcription rates of MDV gC from o ncogenic and attenuated isolates of Md11 were determined. Comparison o f these data with similar studies on MDV proteins whose expression is not altered during attenuation indicates that reduced expression of MD V gC is directly related to reduction in transcription rate of the MDV gC gene in attenuated Md11. Reduced transcription rates and lack of a ny gross structural alterations in the attenuated MDV gC gene suggest that MDV regulatory protein(s) which interact with the MDV gC promoter are altered during attenuation of MDV strain Md11. This conclusion is supported by DNA sequence data which indicate that the promoters of o ncogenic and attenuated Md11 gC genes are identical. (C) 1994 Academic Press, Inc.