NOB1 was first identified in yeast as an essential gene encoding the Nin one binding protein,which is involved in pre-rRNA processing. In a late cytoplasmic processing step,Nob1 cleaves a 20S rRNA intermediate at cleavage site D to produce the mature 18S rRNA. In addition,NOB1 is a crucial molecule in the maturation of the 20S proteasome and protein degradation. It serves as a chaperone to join the 20S proteasome with the 19S regulatory particle in the nucleus and facilitates the maturation of the 20S proteasome. Recently NOB1 has been reported to be overexpressed in several types of cancer,suggesting its involvement in the tumorigenesis.