Binds to the mitochondrial light strand promoter and functions in mitochondrial transcription regulation (By similarity). Component of the mitochondrial transcription initiation complex, composed at least of TFB2M, TFAM and POLRMT that is required for basal transcription of mitochondrial DNA (By similarity). In this complex, TFAM recruits POLRMT to a specific promoter whereas TFB2M induces structural changes in POLRMT to enable promoter opening and trapping of the DNA non-template strand (By similarity). Required for accurate and efficient promoter recognition by the mitochondrial RNA polymerase (By similarity). Promotes transcription initiation from the HSP1 and the light strand promoter by binding immediately upstream of transcriptional start sites (By similarity). Is able to unwind DNA (By similarity). Bends the mitochondrial light strand promoter DNA into a U-turn shape via its HMG boxes (By similarity). Required for maintenance of normal levels of mitochondrial DNA (PubMed:9500544). May play a role in organizing and compacting mitochondrial DNA (PubMed:17581862). May also function as a transcriptional activator or may have a structural role in the compaction of nuclear DNA during spermatogenesis. Monomer; binds DNA as a monomer. Homodimer. Component of the mitochondrial transcription initiation complex, composed at least of TFB2M, TFAM and POLRMT. In this complex TFAM recruits POLRMT to the promoter whereas TFB2M induces structural changes in POLRMT to enable promoter opening and trapping of the DNA non-template strand. Upon metabolic stress, forms a complex composed of FOXO3, SIRT3, TFAM and POLRMT. Interacts with TFB1M and TFB2M. Interacts with CLPX; this enhances DNA-binding. The mitochondrial isoform is widely expressed while the nuclear isoform is testis-specific. Binds DNA via its HMG boxes. When bound to the mitochondrial light strand promoter, bends DNA into a U-turn shape, each HMG box bending the DNA by 90 degrees (By similarity). Phosphorylation by PKA within the HMG box 1 impairs DNA binding and promotes degradation by the AAA+ Lon protease. Embryonic lethal, due to absence of mitochondrial DNA. Mutant embryos die before 10.5 dpc. Truncated N-terminus.