Members of the MTERF (mitochondrial transcription termination factor) family, including MTERF, MTERFD1, MTERFD2 and MTERFD3, are mitochondrial proteins that are that thought to be transcription termination factors. MTERF (mitochondrial transcription termination factor 1) is composed of three leucine zippers that form a three-stranded coiled-coil that binds to DNA. It is suggested that only the phosphorylated form of MTERF has transcription termination activity. MTERFD1 (MTERF domain containing 1) may play a role as a mitochondrial transcription regulator and is expressed as two isoforms produced by alternative splicing. MTERFD2 is a 381 amino acid protein that is encoded by a gene located on human chromosome 2q37.3. MTERFD3 is believed to be involved in cell cycle regulation and cell growth by modulating mitochondrial transcription. MTERFD3 is expressed in heart, skeletal muscle, pancreas and liver.