STRUCTURE AND PROPERTIES OF A HERPESVIRUS OF TURKEYS RECOMBINANT IN WHICH US1, US10 AND SORF3 GENES HAVE BEEN REPLACED BY A LACZ EXPRESSIONCASSETTE

In the process of generating an insertional mutant of herpesvirus of t urkeys (HVT) expressing lacz at the protein kinase (PK) locus, we isol ated a recombinant which contained an intact PK gene but the short uni que regions US1, US10 and SORF3 had been deleted and replaced by the l acZ cassette. Moreover, the virus contained duplicate copies of gD, gI and gE in an opposite orientation flanking lacZ, US2 and PK which wer e contiguous. These results are of interest in relation to the flexibi lity of the short unique segment (U-S) and of the inverted repeats fla nking U-S of the alpha-herpesviruses. The recombinant expressed beta-g alactosidase and was genetically stable in vitro and in vivo. Chickens inoculated with the virus developed antibodies to HVT antigens and to beta-galactosidase but the replication of the recombinant in vivo was impaired in comparison to parental HVT as shown by a reduction in the proportion of infected lymphocytes.