PHOSPHORYLATION AND UBIQUITINATION OF THE 26S PROTEASOME COMPLEX

This article reviews recent studies from our laboratory on protein reg ulators of the proteasome (multicatalytic proteasome complex) in red b lood cells. A 240-kD inhibitory component (CF-2) exists in 26S proteas ome complexes in a form which is conjugated to ubiquitin. Interestingl y, this factor was shown to be identical to delta-aminolevulinic acid dehydratase (ALAD), involved in heme synthesis. A distinct 200-kD inhi bitor of the proteasome is not present in the 26S complex. A 32-kD sub unit of the 20S proteasome appears to be important for the latency of this core protease. Multiple isoelectric variants of the 32-kD subunit are consistent with phosphorylation. Another 20S proteasome subunit o f 30 kD molecular weight is phosphorylated at specific serine residues by copurifying casein kinase II. It is suggested that ubiquitination and phosphorylation may account for at least part of the ATP dependenc y associated with the 26S proteasome complex. These modifications may play a role in the activity, assembly, translocation and/or turnover o f this particle.