Abstract
The mechanism by which a signal recognition particle (SRP) and its receptor mediate protein targeting to the endoplasmic reticulum or to the bacterial plasma membrane is evolutionarily conserved. In Escherichia coli, this reaction is mediated by the Ffh/4.5S RNA ribonucleoprotein complex (Ffh/4.5S RNP; the SRP) and the FtsY protein (the SRP receptor). We have quantified the effects of 4.5S RNA on Ffh-FtsY complex formation by monitoring changes in tryptophan fluorescence. Surprisingly, 4.5S RNA facilitates both assembly and disassembly of the Ffh-FtsY complex to a similar extent. These results provide an example of an RNA molecule facilitating protein-protein interactions in a catalytic fashion.
Comment
This was interesting work carried out by Paul Peluso in Peter Walter's lab at UCSF. The observation that prompted it was that interaction between Ffh and FtsY occurred in the absence of RNA, contrary to previous belief, if the conditions for the assay were manipulated such that the proteins were in excess. He set out to understand the kinetic basis for this behavior, and found that the 4.5S RNA component of SRP appeared to stimulate both assembly and disassembly of the complex. He went on to study the kinetics in more detail.