Canonical primary microRNA (pri-miRNA) precursors are transcribed by RNA 
polymerase II and then processed by the Drosha endonuclease to generate 
approximately 60 nt pre-miRNA hairpins. Pre-miRNAs in turn are cleaved by Dicer 
to generate mature miRNAs. Previously, some short introns, called miRtrons, were 
reported to fold into pre-miRNA hairpins after splicing and debranching, and 
miRNAs can also be excised by Dicer cleavage of rare endogenous short hairpin 
RNAs. Here we report that the miRNAs encoded by murine gamma-herpesvirus 68 
(MHV68) are also generated via atypical mechanisms. Specifically, MHV68 miRNAs 
are transcribed from RNA polymerase III promoters located within adjacent viral 
tRNA-like sequences. The resultant pri-miRNAs, which bear a 5' tRNA moiety, are 
not processed by Drosha but instead by cellular tRNase Z, which cleaves 3' to 
the tRNA to liberate pre-miRNA hairpins that are then processed by Dicer to 
yield the mature viral miRNAs.