GNL1 (guanine nucleotide-binding protein-like 1) is a nuclear protein that likely acts as a regulator of the histocompatibility cluster. GNL1 and MMR1, the murine homolog, are localized within or close to the MHC class I region and belong to the MMR1/HSR1 GTP-binding protein family. GTPases, such as GNL1, from the MMR1/HSR1 GTP-binding protein subfamily are circularly rearranged G-motifs that play a critical role in maintaining normal cell growth. Deletion of these genes results in severe growth defects with a marked reduction in mature rRNA species and a concomitant accumulation of the 35S pre-rRNA transcript. Deletion also causes the ribosomal protein RPL25A to fail exportation from the nucleolus. Deletion of any of the G-domain motifs will result in a null phenotype and nuclear/nucleolar localization that lacks the nucleolar export of preribosomes and is accompanied by a distortion of the nucleolar structure. Upon DNA damage GNL1 is phosphorylated by a kinase, possibly Atm or ATR.