Identification of a novel human nuclear-encoded mitochondrial poly(A) polymerase. Nucleic Acids Res

We report here on the identification of a novel human nuclear-encoded mitochondrial poly(A) polymerase. Immunocytochemical experiments confirm that the enzyme indeed localizes to mitochondrial compart-ment. Inhibition of expression of the enzyme by RNA interference results in significant shortening of the poly(A) tails of the mitochondrial ND3, COX III and ATP 6/8 transcripts, suggesting that the investigated protein represents a bona fide mitochondrial poly(A) polymerase. This is in agreement with our sequencing data which show that poly(A) tails of several mito-chondrial messengers are composed almost ex-clusively of adenosine residues. Moreover, the data presented here indicate that all analyzed mitochon-drial transcripts with profoundly shortened poly(A) tails are relatively stable, which in turn argues against the direct role of long poly(A) extensions in the stabil-ization of human mitochondrial messengers