Abstract

Human mitochondria contain their own genome that is transcribed and all the mt-mRNAs so produced translated, within the organelle. There is a specific machinery required for intraorganellar protein synthesis that has similarities and differences to that of bacteria and the eukaryotic cytosol. The proteins that are involved in the termination step that facilitates release of the nascent peptide are of particular interest. These so called release factors (RF) need to be able to discriminate between sequences in the ribosomal A-site and recognize which are STOP codons. On interaction with the ribosome the RF changes conformation and facilitates hydrolysis of the ester bond that anchors the newly made protein to the final tRNA. Bioinformatic searches have now revealed a family of 4 predicted human mitochondrial release factors, with ICT1 and C12orf65 added to the previously described mtRF1 and mtRF1a. Intriguingly, these 2 new members, ICT1 and C12orf65, both lack the 2 regions involved in codon recognition and are therefore unlikely candidates for RNA triplet recognition.