dnaN is the gene that codes for the DNA clamp (also known as β sliding clamp) of DNA polymerase III in prokaryotes. The β clamp physically locks Pol III onto a DNA strand during replication to help increase its processivity. The eukaryotic equivalent to the β clamp is PCNA.
^PDB1MMI; Oakley AJ, Prosselkov P, Wijffels G, Beck JL, Wilce MC, Dixon NE (July 2003). "Flexibility revealed by the 1.85 Å crystal structure of the beta sliding-clamp subunit of Escherichia coli DNA polymerase III". Acta Crystallogr. D Biol. Crystallogr.59 (Pt 7): 1192–9. doi:10.1107/S0907444903009958. PMID12832762.