During translation initiation in prokaryotes, a GTP molecule is needed in:
During translation initiation in prokaryotes, a GTP molecule is needed in:
formation of formyl-met- $t$ RNA
binding of $30 \mathrm{~S}$ subunit of ribosome with $m$ RNA
association of $30 \mathrm{~S} m \mathrm{RNA}$ with formyl-mel- $t$ RNA
association of $50 \mathrm{~S}$ subunit of ribosome with initiation complex
Solution
Formyl-met-tRNA is formed by addition of methionine to tRNA fMet (formyl-methionine specifictRNA) by the fMet-tRNA synthetase to produce methioninetRNA and then transfer of formyl group from N10 formyl tetrahydrofolate to the amino group of the Met residue to produce $\mathrm{N}$-formyl methionine tRNA. Binding of $30 \mathrm{~S}$ ribosomal subunit to two initiation factors, IF-1 and IF-3 initiates translation. Factor IF-3 prevents the $30 \mathrm{~S}$ and $50 \mathrm{~S}$ subunits from combining prematurely and mediated binding of mRNA to $30 \mathrm{~S}$ subunit. This is followed by binding of complex consisting of the $30 \mathrm{~S}$ ribosomal subunit, IF-3, and mRNA with the initiating formyl met tRNA in presence of GTP-bound IF-2. The pairing of anticodon of tRNA with the mRNAs initiation codon induces binding of $50 \mathrm{~S}$ ribosomal subunit. Thus, association of $30 \mathrm{~S}$ mRNA with formyl-met-tRNA required GTP.