MTERF3, the most conserved member of the mTERF-family, is a modular factor involved in mitochondrial protein synthesis

The MTERF-family is a wide family of proteins identified in Metazoa and plants which includes the known mitochondrial transcription termination factors. With the aim to shed light on the function of MTERF-family members in Drosophila, we performed the cloning and characterization of D-MTERF3, a component of the most conserved group of this family. D-MTERF3 is a mitochondrial protein of 323 amino acids. Sequence analysis in seven different organisms showed that the protein contains five conserved “mTERF-motifs”, three of which include a leucine zipper-like domain. D-MTERF3 knock-down, obtained by RNAi in D.Mel-2 cells, did not affect mitochondrial replication and transcription. On the contrary, it decreased to a variable extent the rate of labelling of about half of the mitochondrial polypeptides, with ND1 being the most affected by D-MTERF3 depletion. These results indicate that D-MTERF3 is involved in mitochondrial translation. This role, likely based on protein–protein interactions, may be exerted either through a direct interaction with the translation machinery or by bridging the mitochondrial transcription and translation apparatus.