Figure 1. Fraction of PEGylated nascent chains for the different ribosome-nascent-chain constructs.

(a) Illustration of key features of the different nascent-chain constructs. The arrested nascent chains are either 95 or 190 residues in length, with a stretch of 10 Ala or Gly residues (red rectangle) that are either two or three residues (black circles) removed from the P-site. The reporter cysteine (blue circle) is at residue position 32 (top) or 33 (bottom) from the PTC. Thus, the nomenclature 3Gly10 indicates that the 10 glycine stretch starts 3 residues removed from the P-site. (b) The fraction of PEGylated nascent chains (F_peg for the extended TM sequence (Table 1) as a function of the number of residues the reporter cysteine is removed from the PTC. This is a cysteine scanning experiment – the identities of all other residues remain the same, but the Cys is substituted in at different positions along the TM sequence, as illustrated by the inset ribosomes. A high fraction of PEGylation corresponds to high accessibility of the reporter cysteine to the PEG molecule. (c) Fraction of PEGylated nascent chains for each nascent chain construct (Table 1) that are either 95 (black) or 190 (gray) residues in length