THE ATTENUATED V60 STRAIN OF CHANNEL CATFISH VIRUS POSSESSES A DELETION IN ORF50 CODING FOR A POTENTIALLY SECRETED GLYCOPROTEIN

A wild-type strain of channel catfish virus was compared at the genomi c level with the attenuated strain V60. In addition to several minor d ifferences, restriction mapping revealed one major deletion (approxima tely 1200 bp) in ORF50 of the V60 strain. Cloning and sequencing of pa rt of this ORF confirmed the presence of a 1164-bp deletion. It should result in a protein of 282 amino acids instead of 670. The predicted truncated protein lacks most of a threonine-rich, highly repetitive re gion in its central part Since the protein encoded by ORF50 possesses a hydrophobic N-terminal leader sequence and no membrane anchor sequen ce, we suggest that it could be a secreted glycoprotein. This protein might be N-glycosylated (35 potential sites) and, given the repetitive arrangement of its residues (mainly threonines), also heavily O-glyco sylated like the mucin-type glycoproteins. The deletion observed in OR F50 of the V60 strain implies the loss of 24 potential N-glycosylation sites and should considerably reduce the extent of O-glycosylation. ( C) 1996 Academic Press, Inc.