RNase H1 promotes replication fork progression through oppositely transcribed regions of mitochondrial DNA.

Mitochondrial DNA (mtDNA) replication uses a simple core machinery similar to those of bacterial viruses and plasmids, but its components are challenging to unravel. Here, we found that, as in mammals, the single gene for RNase H1 () has alternative translational start sites, resulting in two polypeptides, targeted to either mitochondria or the nucleus. RNAi-mediated knockdown did not influence growth or viability of S2 cells, but compromised mtDNA integrity and copy number.