Herpesvirus-dependent amplification and inversion of cell-associated viral thymidine kinase gene flanked by viral a sequences and linked to an origin of viral DNA replication.

The genome of herpes simplex virus 1 or 2 consists of two components, L and S, which invert relative to each other during infection. As a result, viral DNA consists of four equimolar populations of molecules differing solely in the relative orientations of the L and S components. Previous studies have shown that the a sequences, located in the same orientation at the genomic termini and in inverted orientation at the L-S junction, play a key role in the inversion of L and S components. In this report we describe a virus-dependent system designed to allow identification of the viral genes capable of acting in trans to invert DNA flanked by inverted copies of a sequences. In this system, cells are converted to the thymidine kinase-positive phenotype with a chimeric plasmid carrying the thymidine kinase gene flanked by inverted copies of the a sequence and linked to an origin of viral DNA replication derived from the S component. The DNA introduced into the cells is retained and propagated in its original sequence arrangement as head-to-tail concatemers. Infection of these cells with herpes simplex virus 1 or 2 results in as much as 100-fold amplification of the plasmid sequences and inversion of the DNA flanked by copies of the a sequence. In infected cells, the amplified resident DNA accumulates in head-to-tail concatemers and no rearrangement other than the inversions could be detected. These results suggest that the a sequence-dependent inversions required trans-acting viral gene products.