The function of POLR1H (RNA polymerase I subunit H, Ensembl gene identifier ENSG00000066379) is as follows. Core component of RNA polymerase I (Pol I), a DNA-dependent RNA polymerase which synthesizes ribosomal RNA precursors using the four ribonucleoside triphosphates as substrates. Can mediate Pol I proofreading of the nascent RNA transcript. Anchors into the Pol I active site to monitor transcription fidelity and cleave mis- incorporated 5'-ribonucleotides. {ECO:0000269|PubMed:34671025, ECO:0000269|PubMed:34887565, ECO:0000269|PubMed:36271492}.