IDENTIFICATION AND CHARACTERIZATION OF AN ORF VIRUS HOMOLOG OF THE VACCINIA VIRUS GENE ENCODING THE MAJOR ENVELOPE ANTIGEN P37K

DNA sequence analysis of a 1.55-kb region located 10 kb from the left end of the orf virus NZ-2 strain (OV NZ2) genome revealed an open read ing frame, B2L, encoding a protein with a predicted molecular weight o f 41.67 kDa. This protein (p42K) shows 42% amino acid sequence identit y to the vaccinia virus (VAC) major envelope antigen p37K. In addition , p42K shows homology to a protein encoded by molluscum contagiosum vi rus (42.8% identity) and another encoded by fowlpox virus (38.3% ident ity). These proteins are themselves homologues of the VAC p37K. B2L is actively transcribed after the onset of DNA replication and S1 nuclea se analysis mapped the 5' end of the transcript to within the sequence TAAATG. A VAC recombinant capable of expressing the p42K gene was con structed and used as an antigen in radioimmune precipitations and lymp hocyte transformation assays. These assays demonstrated that OV p42K i s one of a limited number of OV proteins to which sheep mount a strong antibody response and which stimulate lymphocytes derived from draini ng lymph nodes following a natural infection with OV NZ2. (C) 1994 Aca demic Press, Inc.