The MTPAP gene encodes an enzyme belonging to the DNA polymerase type-B-like family. The polymerase is responsible for the processes of mRNA polyadenylation, and synthesis of 3’ homopolymeric poly(A) extensions on mitochondrial mRNA transcripts. In vitro studies have found that knockdown of the MTPAP gene leads to extreme shortening of the poly(A) tails on mitochondrial mRNAs. MTPAP is also involved in the replication-dependent histone mRNA catabolic process.
The gene is associated with Spastic Ataxia 4, Autosomal Recessive (SPAX4), a neurodegenerative disorder characterized by progressive cerebellar ataxia, spastic paraparesis, dysarthria, and optic atrophy.