FIG. 1.

(Top) Schematic representation of the 17syn+ HpaI fragment R (bp 117009 to 120300). The internal long repeat (IRL) is indicated by a heavy black bar and the LAT promoter, start site of the primary LAT RNA, and 5′ end of the 2-kb LAT intron are shown. (Middle) Schematic representation of the same region from the LAT null mutants 17-AH, 17-FA91, and 17-FA94. The deletion removes the entire LAT promoter, start site of the primary LAT RNA, as well as the splice donor for the stable LAT introns. (Bottom, left) Viral DNA was cleaved with BamHI, electrophoresed on 0.8% agarose gels, Southern blotted, and probed with a ³²P-labeled probe (bp 120300 to 120468). The presence of the deletion in both the BamHI fragment B (bp 113322 to 123461) and BamHI fragment E (bp 2905 to 11818) confirms that both copies of the LAT locus were mutated in isolates 17-AH and 17-FA94. Similarly, both copies of the LAT locus were genomically restored to wild type in isolates 17-AHRI and 17-AHR2, as evidenced by the wild-type migration of both hybridizing fragments. (Bottom, right) Fragments equivalent to the HpaI fragment R (from BamHI fragment B) and S (from BamHI fragment E) of 17syn+ were cloned from the genome of 17-AH and sequenced. Both strands of both fragments were sequenced. Shown is the region of the gel that confirms the presence of the deletion.