Mammalian mitochondrial DNA sequences can function as in vivo bacterial transcription terminators

We have used a prokaryotic terminator identification vector, pDR721, to isolate regions from rat mitochondrial DNA (mtDNA) that can act as transcription terminators in vivo. Three independent fragments having terminator capability have been mapped to three general regions of the mitochondrial genome. Two terminators, pRMT1 and pRMT3, are found within and around the D-loop and cytochrome b gene, respectively, while the third, pRMT5, is located at the 3'-end of the 16S ribosomal RNA gene. After subcloning into host cells which carried temperature sensitive mutations in the termination factor, rho protein, galactokinase assays at the permissive and non-permissive temperatures suggested that pRMT3 acted as a rho-independent termination element while the other two, pRMT1 and pRMT5, were dependent on rho protein (or a rho-like protein) for efficient transcription termination.