The peak region of 13q contains POLR1D, a subunit of both RNA polymerases I and III. RNA polymerase I is involved in the production of 18S, 5.8S, and 28S rRNAs, while RNA polymerase III synthesizes small essential RNAs, such as tRNAs, 5S rRNA, and some snRNAs.There is not much information regarding this gene in the literature. POLR1D is overexpressed in 42% of the primary tumors, showing high correlation between expression and copy number.

RPA16 cDNA encoding the 16-kDa subunit of mouse RNA polymerase I by a yeast two-hybrid system using mRPA40 as a bait. The deduced amino acid sequence shows 45% identity to the yeast subunit of RNA polymerases I and III, known to associate with AC40, and a local similarity to bacterial alpha subunit.