Expression and subcellular localization of mouse 20S proteasome activator complex PA28

We have cloned the mouse PA28 proteasome activator cDNAs, Northern blot demonstrates high PA28 mRNA levels in liver, kidney and lung, mRNA levels are low in thymus, spleen and brain, In contrast, PA28 protein levels vary little between these tissues, Immunocytological analysis and cell fractionation experiments demonstrate. that both subunits are almost equally distributed between the cytoplasm and the nucleus, Interestingly, PA28 alpha spares nucleoli, while PA28 beta is strongly enhanced in. the nucleolus, This indicates for the first time that the PA28 alpha and PA28 beta subunits may serve nuclear functions which may be different from and independent of each other, (C) 1997 Federation of European Biochemical Societies.