The yeast nucleolar protein NOP7 is necessary for the maturation of 66S preribosomes and interacts with numerous other proteins. One such protein is an essential, conserved WD repeat protein, NOP seven-associated protein 1 (NSA1), that is also required for the yeast 66S ribosome assembly.  NSA1 is also associated with the AAA ATPase Rix7, and release of NSA1 from a novel late nucleolar pre-60S requires the Rix7 function. NSA1 has also been found upregulated in mammalian cancer cells, suggesting it may also play a role in cell proliferation.