The ribosome-bound initiation factor 2 recruits initiator tRNA to the 30S initiation complex.
Bacterial translation initiation factor 2 (IF2) is a GTPase that promotes the binding of the initiator fMet-tRNA(fMet) to the 30S ribosomal subunit. It is often assumed that IF2 delivers fMet-tRNA(fMet) to the ribosome in a ternary complex, IF2.GTP.fMet-tRNA(fMet). By using rapid kinetic techniques, we show here that binding of IF2.GTP to the 30S ribosomal subunit precedes and is independent of fMet-tRNA(fMet) binding. The ternary complex formed in solution by IF2.GTP and fMet-tRNA is unstable and dissociates before IF2.GTP and, subsequently, fMet-tRNA(fMet) bind to the 30S subunit. Ribosome-bound IF2 might accelerate the recruitment of fMet-tRNA(fMet) to the 30S initiation complex by providing anchoring interactions or inducing a favourable ribosome conformation. The mechanism of action of IF2 seems to be different from that of tRNA carriers such as EF-Tu, SelB and eukaryotic initiation factor 2 (eIF2), instead resembling that of eIF5B, the eukaryotic subunit association factor.
Milon
Pohl
P
Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany.
Carotti
Marcello
M
Konevega
Andrey L
AL
Wintermeyer
Wolfgang
W
Rodnina
Marina V
MV
Gualerzi
Claudio O
CO
D031541:Fluorescence Resonance Energy Transfer; D007700:Kinetics; D008954:Models, Biological; D039881:Prokaryotic Initiation Factor-2 / Q000378:metabolism*; D012358:RNA, Transfer, Met / Q000378:metabolism*; D054680:Ribosome Subunits, Small, Bacterial / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
D039881:Prokaryotic Initiation Factor-2; D012358:RNA, Transfer, Met; C089238:fMet-tRNA(fMet)