||Yewdell JW, Reits E, Neefjes J. Making sense of mass destruction: quantitating MHC class I antigen presentation. Nat Rev Immunol. 2003 Dec3(12):952-61. DOI: 10.1038/nri1250 p.958 right column bottom paragraphPubMed ID14647477
|| Reits, E. et al. Peptide diffusion, protection, and degradation in nuclear and cytoplasmic compartments before antigen presentation by MHC class I. Immunity 18, 97–108 (2003)PubMed ID12530979
||Primary source  abstract: "[Investigators] have visualized the fate and dynamics of intracellular peptides in living cells."
||P.958 right column bottom paragraph: "Even so, given the density of ribosomes in the cytoplasm (on average each is within its own diameter of a neighbouring ribosome) and the rapid rate of diffusion of proteasomes (0.3 µm^2/sec) [primary source], it would still be possible for proteasomes to travel to ribosomes within milliseconds. Given the relatively slow rate of translation, proteasomes should collide many times with proteins as they emerge from the ribosome unless they are properly protected by chaperones. Improper shielding could therefore result in co-translational degradation of the still unfolded protein substrate by the proteasome, which is known to be capable of degrading substances in a ubiquitin-independent manner, albeit shown for only one example [ref 68]." Please note-value of 3µm^2/sec for peptide is given in primary source, value for proteasome not located