engleski

HSV-1 miR-H1 is derived from the 0.7 kb transcript arising from the region upstream of the LAT promoter

Herpes simplex virus 1 (HSV-1) expresses many miRNA, some of which are differentially expressed during productive and latent infection. One such miRNA, miRNA-H1, is abundantly expressed during productive infection but almost undetectable in latently infected neurons. Interestingly, miR-H1 is perfectly complementary to another miRNA, miR-H6, expressed at the same locus but from the opposite strand. The function and the primary transcript of miR-H1, including its regulation of expression, are not known. To determine the primary transcript, which gives rise to miR-H1, we analyzed RNA from cells infected with HSV-1 applying different approaches. First, by Northern blot using strand specific probes spanning the miR-H1 locus we detected transcripts of 0.4 and 0.7 kb arising in that region. Both transcripts show late gene expression kinetics, which coincides with the previously established expression kinetics of miR-H1. Next, using rapid amplification of cDNA ends (RACE) technique we have determined 5’ and 3’ end of a putative miR-H1 transcripts arising in the region upstream of the LAT (latency associated transcript) promoter. Our results indicate that 0.4 kb and 0.7 kb transcript have a common transcription termination site (TTS) but different transcription start sites (TSS). An alternative to the autonomous transcriptional unit hypothesis, shorter transcript might also represent a byproduct of the pri-miR-H1 processing or a degradation product. To further investigate the TSS and TTS we applied three different web-based prediction tools. Our analysis indicate a promoter in the vicinity of the 5’ end of 0.7 kb transcript, but not the 0.4 kb transcript. To test if the predicted promoter region has indeed the promoter activity we cloned the region spanning the promoter upstream of the luciferase gene and tested its activity. Moreover, to additionally confirm the activity of the promoter, we have generated mutant viruses with inserted transcriptional termination signal derived from SV40 virus downstream (i.e. blocking its activity) or upstream (i.e. not affecting its activity) of the putative promoter within the virus genome, and we are currently testing the expression of miR-H1 in these mutants. Our results will reveal the transcriptional control of miR-H1 and will represent a base for further studies of roles of miR-H1 in HSV-1 infection.

miR-H1, transcript, promoter

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