The nucleolar protein Nop19p interacts preferentially with Utp25p and Dhr2p and is essential for the production of the 40S ribosomal subunit in Saccharomyces cerevisiae.

In eukaryotes, ribosome biogenesis is a process of major interest that requires more than 200 factors acting coordinately in time and space. Using genetic and proteomic studies, most of the components have now been identified. Based on its nucleolar localization, we characterized the protein encoded by the open reading frame YGR251W, we renamed Nop19p as playing an essential role in ribosome biogenesis. Depletion of the Nop19p in yeast impairs pre-rRNA processing at sites A₀, A₁ and A₂, leading to a strong decrease in 18S rRNA and 40S subunit levels. Nop19p is a component of 90S preribosomes which assembly is believed to result from stepwise incorporation of UTP modules. We show that Nop19p depletion does not impair the incorporation of UTP subcomplexes on preribosomes and conversely that depletion of UTP subcomplexes does not affect Nop19p recruitment on 90S preribosomes. TAP experiments under stringent conditions revealed that Nop19p interacts preferentially with the DEAH-box RNA helicase Dhr2p and Utp25p, both required for A 0, A 1 and A 2 cleavages. Nop19p appeared essential for the incorporation of Utp25p in preribosomes. In addition, our results suggest that in absence of Nop19p, Dhr2p remains trapped within aberrant preribosomes.