Influence of TF on the conformation of ribosome-bound SRP. Changes of distances upon binding of TF to the complex of SRP with RNC (A) or vacant ribosomes (B) were measured by FRET. Distances between the indicated positions in M and NG domains, labeled with OG, and the 3′ end of 4.5S RNA21–81, labeled with Alx 647, were measured in free SRP (white bars), SRP-RNC or SRP-ribosome (gray bars), and SRP-RNC-TF or SRP-ribosome-TF (black) complexes.