Functional ramifications of FRET-detected nascent chain folding far inside the membrane-bound ribosome.

During protein biosynthesis, nascent protein chains are directed along a long narrow tunnel that spans the large ribosomal subunit. It has recently become clear that this structural feature has evolved to effect regulatory control over aspects of protein synthesis and protein trafficking. Since this control is nascent chain-specific, ribosomal components that form the tunnel must be involved in recognizing selected nascent proteins as they pass by. The present study focuses on one such situation in which nascent secretory proteins and membrane proteins are distinguished by the ribosome-induced folding of the latter's hydrophobic transmembrane sequence far inside the ribosomal tunnel and close to the peptidyltransferase centre.