Question

Fakunding and Hershey mixed [³²P]IF2 (blue) and [³H]fMet-tRNAfMet (red) with 30S ribosomal subunits to form 30S initiation complexes. Then they added 50S ribosomal subunits in the presence of either (a) GDPCP, or (b) GTP, and then analyzed the complexes by sucrose gradient ultracentrifugation. How to interpret the results that there is difference for the binding of IF2 to the ribosome between the addition of GTP and GDPCP in the experiments?

GDPCP 10F 70s 30s GTP F 705 305 10 (32P]IF 2 (pmol) H]fMet-tRNA (pmol) IIIIIIIII 10 10 20 30 20 30 0 Fraction number Figure 17.10 Effect of GTP hydrolysis on release of IF2 from the ribosome. Fakunding and Hershey mixed [P]IF2 (blue) and [H] fMet-tRNAMet (red) with 30S ribosomal subunits to form 30S initiation complexes. Then they added 50S ribosomal subunits in the presence of either (a) GDPCP, or (b) GTP, and then analyzed the complexes by sucrose gradient ultracentrifugation as in Figure 17.8. (Source: Adapted

Answer 1

IF2 is a g-protein that plays a crucial role in the initiation of procaryotic protein synthesis. It interacts directly with the fmet-tRNA met, and initiates decoding in the p-site.IF2 promotes the fast formation of the first peptide bond in the presence of GTP, but it could not form a bond with GDPCP, because GDPCP_IF2 binds strongly to the post-initiation ribosomes.GTP form of IF2 accelerates the formation of the 70s ribosome from subunits as GTP hydrolysis is essential for the release of IF2. Rapid GTP hydrolysis by IF2 drives the transition to the elongation-competent conformation, thus committing the ribosome to enter the elongation cycle.