ribosome-bound nascent chains 1.1±0.07%: completed, newly made polypeptides 0.5±0.04% %
||Budding yeast Saccharomyces cerevisiae
||Duttler S, Pechmann S, Frydman J. Principles of cotranslational ubiquitination and quality control at the ribosome. Mol Cell. 2013 May 9 50(3):379-93. doi: 10.1016/j.molcel.2013.03.010. p.381 right column top paragraphPubMed ID23583075
||P.381 left column bottom paragraph: "All ubiquitinated material was depleted after the first round of polyUb-affinity isolation (Figure S1F), demonstrating that the polyUb-affinity resin was not limiting in [investigators’] experiments. Along with the experiments in Figures S1A and S1B, [they] conclude that the polyUb affinity approached used here quantitatively isolates polyubiquitinated polypeptides from the RNC [ribosome-nascent chain complex] fraction. The direct polyubiquitination of nascent chains was further confirmed in two additional experiments. First, 35S-nascent chains were released from purified RNCs, and then polyUb-affinity isolation was carried out after an additional round of sucrose cushion sedimentation for the separation of vacant ribosomes from the released nascent chains (Figure 1E, lane 6 Figure S2). This demonstrates that released nascent chains are directly captured by the polyUb-affinity resin. Second, [they] subjected isolated ribosome-35S-nascent chain complexes to a stringent salt wash (Fleischer et al., 2006) to remove associated factors prior to the ribosome dissociation step, and subsequent polyUb-affinity isolation confirmed that these salt-stripped nascent chains were ubiquitinated (Figure S1G, lanes 6 and 8 and lanes 10 and 12). Altogether, these experiments demonstrate that nascent chains are directly ubiquitinated while on the ribosome."
||P.381 right column top paragraph: "Quantitative analysis showed that approximately 1.1% ± 0.07% (n = 59) of the ribosome-bound nascent chains and 0.5% ± 0.04% (n = 59) of completed, newly made polypeptides were ubiquitinated in vivo (Figure 1F). [Investigators] conclude that newly made proteins are ubiquitinated co- and post-translationally during synthesis."