Schematic diagram of ubiquitin and SUMO modification pathways

1. Schematic diagram of ubiquitin and SUMO modification pathways small polypeptides that are usually conjugated to internal lysine residues of target proteins through their C-terminal glycine residues, forming isopeptide bonds

2. THE UBIQUITIN–PROTEASOME PATHWAY Degradation of the tagged substrate by the 26S proteasome conjugation of ubiquitin to the target molecule

3. HIERARCHICAL STRUCTURE OF THE UBIQUITIN-CONJUGATING MACHINERY

4. MODES OF RECOGNITION OF PROTEIN SUBSTRATES BY DIFFERENT E3S

5. MODES OF RECOGNITION OF PROTEIN SUBSTRATES BY DIFFERENT E3S. An E3 can recognize a substrate constitutively via a primary motif such as the N-terminal residue (N-end rule). Many proteins are recognized following post-translational modification (e.g. phosphorylation) or association with an ancillary protein (e.g. Hsc or HPV-E6). N-R, N-terminal receptor.

6. Small Ubiquitin-like Modifier or SUMO proteins are a family of small proteins that are covalently attached to and detached from other proteins in cells to modify their function. SUMOylation is a post-translational modification involved in various cellular processes, such as nuclear-cytosolic transport, transcrptional regulation, apoptosis, protein stability, response to stress, and progression through the cell cycle SUMO proteins are similar to ubiquitin, and SUMOylation is directed by an enzymatic cascade analogous to that involved in ubiquitination. In contrast to ubiquitin, SUMO is not used to tag proteins for degradation

7. XPC may participate in BER of GT mismatches ontributing to the supression of spontaneous mutations that may be one of the factors promoting carcinogenesis in xeroderma pigmentosum Bergink and Jantsch Nature, 2009