U3 Small Nucleolar Ribonucleoprotein 23, Homolog (UTP23)

One of those complexes, the SSU processome, is required for pre-18S rRNA maturation. Although many of its components have been identified, the endonucleases that cleave the pre-18S rRNA have remained mysterious.

Utp23, a protein homologous to the PINc domain protein Utp24. Utp23 and Utp24 are essential nucleolar proteins and previously undescribed components of the SSU processome. In that sense, both Utp23 and Utp24 are required for the first three cleavage steps in 18S rRNA maturation. In addition, single-point mutations in the conserved putative active site of Utp24 but not Utp23 abrogate its function in ribosome biogenesis. Utp24 might be the elusive endonuclease that cleaves the pre-rRNA at sites A(1) and/or A(2.).