Atypical splicing of the latency-associated transcripts of herpes simplex type 1.

We previously have shown that two latency-associated transcripts (LATs) of herpes simplex type 1 (HSV-1) are probably lariats, produced during splicing. By RNaseH digestion analysis, we now show that the major branchpoint of the 2.0-kb LAT was within 46 nt 5' of the splice acceptor site. A more detailed mapping by primer extension revealed the branchpoint as an adenosine 29 nt 5' of the splice acceptor site. Introduction of two branchpoint sequences with good matches to the consensus at position -25 had no effect on the splicing efficiency but reduced the accumulation of the 2.0-kb LATs at least 90-fold. The second focus of our studies was the 1.5-kb LAT. It was not detected by Northern analyses in either productively infected or transfected cultured cells or even in cells of neuronal origin. However, it was detected in the trigeminal ganglia of mice experimentally infected with HSV-1 after 10 days. Moreover, its abundance relative to that of the 2.0-kb species increased 4-fold from 10 to 30 days after infection, consistent with an interpretation that the 1.5-kb species, once formed, was more stable than the 2.0-kb species.