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. Author manuscript; available in PMC: 2014 Sep 1.
Published in final edited form as: Cell Biochem Biophys. 2013 Sep;67(1):75–89. doi: 10.1007/s12013-013-9621-9

Figure 2. Measuring proteasome activity.

Figure 2

Proteasome reporters consist of two major elements; a targeting sequence to recruit the reporter to the proteasome (usually a degron) and an analytical handle that can produce a measureable signal (depicted here as the green fluorescent protein (GFP); however other signals such as luciferase or FLAG tags have been used). Ubiquitin-dependent proteasomal targeting uses either the 16 amino acid degron from CL1 (A) or a non-cleavable ubiquitin (B) to measure proteasome activity in response to various conditions such as drug-induced inhibition. (C) The ubiquitin-independent degron ODC is also recruited to the proteasome without requiring the E1-E3 enzymatic cascade. (D) A two component degron demonstrates the importance of an unstructured initiation region for efficient targeting and degradation of reporters. (E) The N-end rule governs N-terminal amino acids that are stabilizing (valine) or destabilizing (arginine).