CDNA CLONING AND FUNCTIONAL-ANALYSIS OF P-28 (NAS6P) AND P40.5 (NAS7P), 2 NOVEL REGULATORY SUBUNITS OF THE 26S PROTEASOME

We employed cDNA cloning to deduce the complete primary structures of p28 and p40.5, two novel subunits of PA700 (also called 19S complex), a 700 kDa multisubunit regulatory complex of the human 26S proteasome. These polypeptides consisted of 226 and 376 amino acids with calculat ed molecular masses of 24 428 Da and 42 945 Da, and isoelectric points of 5.68 and 5.46, respectively. Intriguingly, p28 contained five cons erved motifs known as 'ankyrin repeats', implying that this subunit ma y contribute to interaction of the 26S proteasome with other protein(s ). Computer-assisted homology analysis revealed high sequence similari ties of p28 and p40.5 with yeast proteins, termed Nas6p and Nas7p (non -ATPase subunits 6 and 7), respectively, whose functions are as yet un known. Disruption of these yeast genes, NAS6 and NAS7, had no effect o n cell viability, indicating that neither of the two subunits is essen tial for proliferation of yeast cells. However, the NAS7, but not NAS6 , disruptant cells caused high sensitivity to heat stress, being unabl e to proliferate at 37 degrees C. (C) 1998 Elsevier Science B.V. All r ights reserved.