Proteasomes: multicatalytic proteinase complexes.

The multicatalytic proteinase complex (proteasome) is a highmolecular-mass (approximately 700 kDa) intracellular proteinase which has been isolated under a variety of different names from a wide variety of eukaryotic cells and tissues (reviewed, Rivett, 1989a; Orlowski, 1990). The proteinase complex is composed of at least 24 subunits which include many different polypeptides arranged in a cylindrical structure. Other multi-subunit complexes with cylindrical structures include 'prosomes', that are widely distributed 19 S ribonucleoprotein particles which were thought to be involved in the control of translation (Schmid et al., 1984; Martins de Sa et al., 1986), erythrocyte cylindrin (Harris, 1988), and a number of other partially characterized 16-22 S cylindrical particles. 'Prosomes' and certain related particles have been shown to have proteolytic activity and to share antigenic cross-reactivity with the multicatalytic proteinase (Falkenburg et al., 1988) and are therefore believed to be the same. The particles are most often referred to either as multicatalytic proteinase complexes (Dahlmann et al., 1988; Orlowski and Wilk, 1988) or, more recently, as proteasomes (Arrigo et al., 1988) and their properties are broadly similar irrespective of the