Association of Escherichia coli ribosomes with the inner membrane requires the signal recognition particle receptor but is independent of the signal recognition particle

摘要

In mammalian cells, as well as Escherichia coli ribosomes translat- ing membrane proteins interact cotranslationally with translocons in the membrane, and this interaction is essential for proper insertion of nascent polypeptides into the membrane. Both the signal recognition particle (SRP) and its receptor (SR) are required for functional association of ribosomes translating integral mem- hrane proteins with the translocon. Herein, we confirm that mem- hrane targeting of E. coli ribosomes requires the prokaryotic SRα homolog FtsY in vivo. Surprisingly, however, depletion of the E coli SRP54 homolog (Ffh) has no significant effect on binding of ribosomes to the membrane. although Ffh depletion is detrimental to growth. These and other observations suggest that, in E. coli, SRP may operate downstream of SR-mediated targeting of ribo- somes to the plasma membrane.