Binds preferentially and cooperatively to pyrimidine rich single-stranded DNA (ss-DNA). 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. 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. In addition it is able to promote the 5'-3' unwinding activity of the mtDNA helicase TWNK. May also function in mtDNA repair. Homotetramer. 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. Interacts with POLDIP2. Interacts with PRIMPOL. Expressed in all the layers of the retina (at protein level).