Deletion mutant of a herpesvirus and vaccine containing said virus

A live deletion mutant of a pseudorabies virus derived from a parental strain having a parental genome of about 160,000 nucleotide pairs, said parental genome comprising

• (a) two inverted repeats, each of which contains cleavage sites for the restriction endonucleases BamHI and KpnI, BamHI digestion of the parental genome yielding two pairs of restriction fragments derived entirely from the sequence of the inverted repeats, the larger fragment of each pair being designated as BamHI fragments 5;
• and KpnI digestion of the genome yielding two fragments, designated KpnI fragment E and kpnI fragment H, each of said KpnI fragments containing the distal end of one of the inverted repeats;
• (b) a unique sequence located between the inverted repeats, said unique sequence comprising a BamHI restriction fragment of about 7 kilobase pairs in length designated BamHI fragment 7, said BamHI fragment 7 containing a cleavage site for the restriction endonuclease SalI, wherein cleavage at the SalI site produces two unequal fragments from BamHI fragment 7, one fragment of about five kilobase pairs in length and the other of about two kilobase pairs in length;
• and
• (c) a gene for thymidine kinase, said deletion mutant being characterized by one or more deletions, said deletions being located in
• (i) a portion of an inverted repeat which is common to BamHI fragment 5 and either KpnI fragment E or KpnI fragment H;
• (ii) the about five kilobase pair SalI fragment of BamHI fragment 7, or
• (iii) both.