Nop25 is a 213 amino acid protein that localizes to the nucleolus and is thought to bind to 28S rRNA, possibly playing a role in the processing of rRNA molecules and in the subsequent assembly and maturation of ribosomes. The gene encoding Nop25 maps to human chromosome 22, which houses over 500 genes and is the second smallest human chromosome. Mutations in several of the genes that map to chromosome 22 are involved in the development of Phelan-McDermid syndrome, Neurofibromatosis type 2, autism and schizophrenia. Additionally, translocations between chromosomes 9 and 22 may lead to the formation of the Philadelphia Chromosome and the subsequent production of the novel fusion protein BCR-Abl, a potent cell proliferation activator found in several types of leukemias.