The large subunit has a tunnel about 10 nm long and 2.5 nm in diameter. This tunnel is thought to be the channel that newly assembled polypeptide chains pass through on their way out of the ribosome.
Different views: in yellow the 30S (small) subunit; in blue the 50S (large) subunit.
Landmarks of the 30S subunit: h, head; p, platform; ch, channel presumed to be the conduit for mRNA; sp, spur.
Landmarks of the 50S subunit: CP, central protuberance; St, L7/L12 stalk; L1, L1 protein; IC, interface canyon; T, tunnel presumed to be the conduit for the nascent polypeptide chain; T1 and T2, lower tunnel segments, leading to alternative exit sites E1 and E2, respectively.
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