Mitochondrial Transcription Terminator Family Members mTTF and mTerf5 Have Opposing Roles in Coordination of mtDNA Synthesis

Abstract

All genomes require a system for preventing collisions between the machineries of DNA replication and transcription. We have investigated the roles in this process of two proteins of the mTERF (mitochondrial transcription termination factor) family in Drosophila. These factors, mTTF and mTerf5, share common binding sites in the mitochondrial genome, which we found to coincide with sites of replication pausing. Knockdown of either factor by RNA interference resulted in mtDNA depletion and developmental arrest. mTTF knockdown decreased site-specific replication pausing, but led to an increase in random stalling and regression of replication forks, with impaired synthesis of the lagging strand. This we attribute to random collisions with the transcriptional machinery. Conversely, mTerf5 knockdown led to enhanced replication pausing at mTTF binding sites. These findings indicate an essential and previously undescribed role for proteins of the mTERF family in the integration of transcription and DNA replication, preventing unregulated collisions and facilitating productive interactions between the two machineries that are inferred to be essential for completion of lagging-strand DNA synthesis