Eukaryotic ribosome biogenesis requires the concerted action of ~200 auxiliary protein factors on the nascent ribosome. For many of these factors structural and functional information is still lacking. The endonuclease Nob1 has been recently identified in yeast as the enzyme responsible for the final cytoplasmatic trimming step of the pre-18S rRNA during the biogenesis of the small ribosomal subunit. Here we report the NMR resonance assignments for a Nob1 homolog from the thermophilic archeon Pyrococcus horikoshii as a prerequisite for further structural studies of this class of proteins.