Fig. 4.

Viral interactions with the miRNA pathway. (1) Some viral families, in particular the herpesviruses, express their own miRNAs using the host miRNA processing pathway. Viral miRNAs may regulate host or viral mRNA targets and may be important for viral latency. (2) A positive role for a host miRNA in viral infection has been demonstrated for miR-122 binding to hepatitis C virus RNA. Negative regulation of viral gene expression by host miRNAs has been suggested by some studies, although its relevance in viral infection is not yet clear. (3) Several viruses modulate levels of host miRNAs.