THE FIRST CHARACTERIZATION OF A EUBACTERIAL PROTEASOME - THE 2OS COMPLEX OF RHODOCOCCUS

Background: The 26S proteasome is the central protease of the ubiquiti n-dependent pathway of protein degradation. The proteolytic core of th e complex is formed by the 20S proteasome, a cylinder-shaped particle that in archaebacteria contains two different subunits (alpha and beta ) and in eukaryotes contains fourteen different subunits (seven of the alpha-type and seven of the beta-type).Results: We have purified a 20 S proteasome complex from the nocardioform actinomycete Rhodococcus sp . strain NI86/21. 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 pr eparations reveal the existence of four subunits, two of the alpha-typ e and two of the beta-type, the genes for which we have cloned and seq uenced. Electron micrographs show that the complex has the four-ringed , cylinder-shaped appearance typical of proteasomes. Conclusions: The recent description of the first eubacterial ubiquitin, and our discove ry of a eubacterial proteasome show that the ubiquitin pathway of prot ein degradation is ancestral and common to all forms of life.