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. Author manuscript; available in PMC: 2015 Mar 14.
Published in final edited form as: Curr Opin Struct Biol. 2014 Mar 14;0:156–164. doi: 10.1016/j.sbi.2014.02.002

Figure 3.

Figure 3

The proteasome recognizes substrates in three different modes; ubiquitin-dependent (left), adapter-mediated (middle), and ubiquitin-independent (right) modes. In all three, an intrinsically disordered region in the substrate is recognized by the ATPase motor to allow the proteasome to initiate degradation. This aspect of proteasomal degradation resembles the targeting mechanisms predominant with the bacterial and archaeal analogues of the proteasome. Ubiquitin tags can be either recognized by the two intrinsic proteasome receptors Rpn10 and Rpn13 (left), or by non-stoichiometric proteasome subunits that serve as substrate adaptors such as UbL-UBA proteins (middle). The UbL-UBA proteins might bind substrates by themselves (second right) or together with the intrinsic substrate receptors (second left), which facilitate degradation of various substrates by positioning the disordered region properly. Finally, some substrates may be recognized only by their initiation sites.