Proteasomes reach their mature active state via a complex cascade of folding, assembly and processing events. The Rhodococcus proteasome offers a means to dissect the assembly pathway and to characterize intermediates; its four subunits (α1, α2, β1, β2) assemble efficiently in vitro with any combination of α and β. Assembly studies with wild-type and N-terminally truncated β-subunits in conjunction with refolding studies allowed to define the role of the propeptide which is two-fold: It supports the initial folding of the β-subunits and it promotes the maturation of the holoproteasomes.
Zühl, F., Seemüller, E., Golbik, R., & Baumeister, W. (1997). Dissecting the assembly pathway of the 20S proteasome. FEBS Letters, 418(1–2), 189–194. https://doi.org/10.1016/S0014-5793(97)01370-7