The α4 and α7 subunits and assembly of the 20S proteasome

Abstract
The detailed mechanism of eukaryotic 20S proteasome assembly is currently unknown. In the present study, we demonstrate that the 20S proteasome subunits α4 and α7 interact with each other as well as all the α‐subunits in vivo and in vitro. The N‐terminal parts of α4 and α7 are essential for these newly discovered interactions in vitro. Glycerol gradient centrifugation of soluble extracts of HEK293 cells and Western blot analyses show that several α‐subunits are found in non‐proteasomal low‐density fractions. The α4 and α7 subunits co‐immunoprecipitate together from these low‐density fractions. The unexpected interaction between α4 and α7 may provide a molecular basis for the formation of previously reported 13S and 16S assembly intermediates.