The Signal Recognition Particle (SRP) ribonucleoprotein complex and its membrane-associated receptor (SR) mediate co-translational targeting of membrane and secretory proteins in all organisms.  Ffh, the bacterial SRP54 homolog, recognizes the signal sequence emerging from the         translating ribosome, and the SRP RNA component serves as a platform for the association of Ffh and the SR (FtsY in bacteria). The GTP binding domains of Ffh and FtsY dimerize upon GTP binding. The complex then undergoes a large-scale rearrangement from the initial position at the tetraloop to the distal region of the SRP RNA hairpin where GTP hydrolysis is        triggered and the complex dissociates. This allows the translating ribosome to be delivered to the translocon in a GTP-dependent manner. The crystal structure of the bacterial SRP:SR complex arrested in the cargo release state reveals that the Ffh:FtsY heterodimer bind the 5’,3’ end of the SRP hairpin RNA¹. The high resolution crystal structure of Ffh:FtsY heterodimers bound to SRP RNA at   the tetraloop and the distal region allowed a deeper understanding of the system². The        tetraloop interactions reveal the structural basis of receptor recruitment and rationalize        previously accumulated biochemical data. The distal interactions, in combination with        mutagenesis and biochemical experiments reveal the role of the SRP RNA in stimulation of  GTP hydrolysis. This mechanism couples GTP hydrolysis to conformational changes necessary for signal sequence handoff to the translocon^1,2.