Figure 1.

Model for CCP1/Nna1 function in protein turnover. Intracellular proteins are targeted for degradation by the addition of a polyubiquitin tail and undergo degradation by the 26S proteasome complex. Products of proteasome-mediated degradation are peptides, typically ranging from 10 to 20 aa. These peptides are cleaved by aminopeptidases, as well as other enzymes (oligoendopeptidases, dipeptidases) into amino acids. Hypothesized role for CCP1/Nna1 in peptide turnover is indicated.