Polymerase that creates the 3' poly(A) tail of mitochondrial transcripts. This is not required for transcript stability or translation but may maintain mRNA integrity by protecting 3' termini from degradation. ATP + RNA(n) = diphosphate + RNA(n)-3'-adenine ribonucleotide Mutant male larvae die at the third instar larval stage with a severe reduction in polyadenylation and increased mitochondrial tRNA levels except for tRNA(Cys) which shows a marked reduction and an accumulation of shortened RNAs. Mutant male larvae show de novo translation of some peptides, suggesting that polyadenylation is not required for translation. They also show reduced assembly and activity of repiratory chain complexes I and V. Heterozygous females are viable and fertile as the gene is X-linked. RNAi-mediated knockdown results in reduced larval body weight, death at the ferrate stage or soon after eclosion and severely reduced polyadenylation in larvae. Belongs to the DNA polymerase type-B-like family.