The first characterization of a eubacterial proteasome: the 20S complex of Rhodococcus

Abstract

Background: The 26S proteasome is the central protease of the ubiquitin-dependent pathway of protein degradation. The proteolytic core of the complex is formed by the 20S proteasome, a cylinder-shaped particle that in archaebacteria contains two different subunits (α and β) and in eukaryotes contains fourteen different subunits (seven of the α-type and seven of the β-type). Results We have purified a 20S proteasome complex from the nocardioform actinomycete Rhodococcus sp. strain N186/21. The complex has an apparent relative molecular mass of 690 kD, and efficiently degrades the chymotryptic substrate Suc-Leu-Leu-Val-Tyr-AMC in the presence or absence of 0.05 % SDS. Purified preparations reveal the existence of four subunits, two of the α-type and two of the β-type, the genes for which we have cloned and sequenced. Electron micrographs show that the complex has the four-ringed, cylinder-shaped appearance typical of proteasomes. Conclusion The recent description of the first eubacterial ubiquitin, and our discovery of a eubacterial proteasome show that the ubiquitin pathway of protein degradation is ancestral and common to all forms of life. © 1995 Elsevier Science Ltd. All rights reserved.