Incorporation of nuclear matrix attachment regions into the herpes simplex virus type 1 genome does not induce long-term expression of a foreign gene during latency.

The nuclear matrix plays a critical role in DNA replication, gene transcription and RNA processing. Transcriptionally active genes are usually associated with the nuclear matrix through DNA sequences, matrix attachment regions or MARs, which tether looped DNA to the matrix. In stable transfection and in transgenic mice MAR elements placed at the flanks of genic constructs may enhance expression and insulate against position effect variability, suggesting that independent units of transcription are established insulated from the regulatory controls of their neighbors. Herpes simplex virus type 1 (HSV-1) establishes lifelong latency in the infected host. Latency repression of viral genes extends to foreign genes incorporated into the viral genome. We report here a test of the hypothesis that MAR elements, flanking a foreign gene in the HSV-1 genome, would act to insulate it from latency repression, achieving long-term expression. A recombinant virus was produced which has an expression construct inserted into the HSV-1 genome at the Us3 locus. The expression construct consists of the A MAR element on one flank, an HIV-LRT driving the lacZ gene and the B MAR element on the other flank. The A MAR element is a 3 kb pair fragment of the 5' portion of the chicken lysozyme gene and the B MAR element is a 2.6 kb pair fragment from the 5' end of the human beta-globin gene locus control region. The LTR is derived from a human immunodeficiency virus isolated from the brain of an AIDS patient. Virus was stereotactically injected in the hippocampus, olfactory bulb and striatum of rat brains. Intense blue reaction product indicating beta-galactosidase activity was found in cells in each injected area at 2 days after injection. At 14 days after injection beta-galactosidase activity was no longer detected at any of the injected sites. We conclude that the MAR element construct did not escape latency repression.