The proteasome is the main proteolytic enzyme that functions in the ubiquitin-proteasome system. The 26S proteasome has multi-subunit protease complexes consisting of 20S subunits composed of four seven-numbered rings with two outer rings containing a subunits and two central rings composed of (3 subunits, and 19S caps of 6 ATPase and 11 non-ATPase subunits; however, it is unclear how these subunits are regulated and the 26S proteasomes assembled. To verify whether each subunit's mRNA expression is associated with the mRNA expression of other proteasome subunits, we carried out expression analysis of 34 proteasome subunits mRNA on peripheral blood from 75 subjects. The expression of proteasome subunits mRNA was comparable in each individual of the studied population and the mRNA expression has been investigated in each 20S or 19S proteasome. Our results suggest that each type of subunit is regulated by respectively common factors, and that the 20S and 19S proteasomes are regulated by different systems. (C) 2008 Elsevier Inc. All rights reserved.