Binds preferentially and cooperatively to pyrimidine rich single-stranded DNA (ss-DNA) (PubMed:21953457, PubMed:23290262, PubMed:31550240). In vitro, required to maintain the copy number of mitochondrial DNA (mtDNA) and plays a crucial role during mtDNA replication by stimulating the activity of the replisome components POLG and TWNK at the replication fork (PubMed:21953457, PubMed:12975372, PubMed:26446790, PubMed:15167897, PubMed:31550240). Promotes the activity of the gamma complex polymerase POLG, largely by organizing the template DNA and eliminating secondary structures to favor ss-DNA conformations that facilitate POLG activity (PubMed:26446790, PubMed:21953457, PubMed:31550240). In addition it is able to promote the 5'-3' unwinding activity of the mtDNA helicase TWNK (PubMed:12975372). May also function in mtDNA repair (PubMed:23290262). Homotetramer (PubMed:23290262, PubMed:31550240). Interacts with MPG/AAG, through inhibition of its glycosylase activity it potentially prevents formation of DNA breaks in ssDNA, ensuring that base removal primarily occurs in dsDNA (PubMed:23290262). Interacts with POLDIP2 (PubMed:16428295). Interacts with PRIMPOL (PubMed:25550423). Expressed in retinal ganglion cells, photoreceptors, pigmented epithelium and fibroblasts (at protein level). The disease is caused by variants affecting the gene represented in this entry.