Figure 4.
Three Distinct Conformations of IF3 on 30S PICs
(A) In PIC-2A, the CTD is in position 1 at the P site, while the NTD moves away (arrow; NTD movement is measured using Arg36 as the reference point) from the platform to bind to the elbow of the fMet-tRNAfMet. The linker remains attached to h23 and h24. IF3 from PIC-1C is shown in gray for comparison. Inset shows the movement of the β-hairpin (using Arg159 as the reference) with respect to that in PIC-1C.
(B) In PIC-3, the CTD moves slightly to position 1′ at the P site and the NTD moves ∼27 Å while attached to the elbow of the fMet-tRNAfMet. The linker is no longer in contact with 30S. IF3 from PIC-2A is shown in gray for comparison. Inset shows the movement of β-hairpin with respect to that in PIC-2A.
(C) In PIC-4, the CTD moves ∼25 Å away from the P site to position 2, while the NTD moves while attached to the elbow of the fMet-tRNAfMet. The linker is no longer in contact with 30S. IF3 from PIC-3 is shown in gray for comparison. IF1 is not present in PIC-4, but its location in PIC-3 is shown here to highlight the movement of the CTD away from it.
(D) Superposition of IF3 in PIC-1C (yellow), PIC-2A (cyan), PIC-3 (orange), PIC-4 (red). The fMet-tRNAfMet and IF1 from PIC-3 are shown to highlight the different conformations of CTD and NTD. The movement of the CTD is measured using Arg125 as the reference point. The arrows show the overall direction of movement of the two domains.