COMPARATIVE SEQUENCE-ANALYSIS OF THE LONG REPEAT REGIONS AND ADJOINING PARTS OF THE LONG UNIQUE REGIONS IN THE GENOMES OF HERPES-SIMPLEX VIRUSES TYPE-1 AND TYPE-2

We report the determination of the DNA sequence of the long repeat (R(L)) region and adjacent parts of the long unique (U(L)) region in the genome of herpes simplex virus type 2 (HSV-2) strain HG52. The DNA sequences and genetic content of the extremities of HSV-2 U(L) were found to be closely similar to those determined previously for HSV-1. The 5658 bp sequenced at the left end of HSV-2 U(L) contained coding regions for genes UL1 to UL4 plus part of UL5. The 4355 bp sequenced at the right end of U(L) contained coding regions for part of gene UL53, and the whole of genes UL54 to UL56. Comparison of the HSV-1 and HSV-2 UL56 sequences led to a correction in the published HSV-1 UL56 reading frame. The HSV-2 R(L) region, including one copy of the a sequence, was determined to be 9263 bp, with a base composition of 75-4% G + C and with many repetitive sequence elements. In HSV-2 R(L), sequences were identified corresponding to HSV-1 genes encoding the immediate early IE110 (ICPO) transcriptional regulator and the ICP34.5 neurovirulence factor; the former HSV-2 gene was proposed to contain two introns, and the latter one intron. Downstream of the HSV-2 immediate early gene, the R(L) sequence encoding the latency-associated transcripts (LATs) was found to be dissimilar to that in HSV-1; the probable LAT promoter regions, however, showed similarities to HSV-1. Properties of the LAT sequences in both HSV-1 and HSV-2 were consistent with LATs being generated as an intron excised from a longer transcript.