Cryo-EM study of start codon selection during archaeal translation initiation

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Translation initiation is a fundamental cellular process.
• The ternary complex (TC), comprising eIF2-GTP-Met-tRNAiMet, is central to translation initiation.
• The precise role of eIF2 in start codon selection remains incompletely understood.

Purpose of the Study:

• To elucidate the structural mechanisms by which eIF2 influences start codon selection during translation initiation.
• To present high-resolution cryo-electron microscopy (cryo-EM) structures of the archaeal 30S initiation complex.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to determine the structures.
• Analysis of two distinct conformational states of the ternary complex (TC) bound to the 30S ribosomal subunit.

Main Results:

• Two conformational states of the TC were observed: a relaxed state with tRNA outside the P site and a constrained state with tRNA in the P site.
• TC constraint is stabilized by codon/anticodon base pairing.
• In the absence of a start codon, eIF2 actively swings the tRNA out of the P site.

Conclusions:

• A 'spring force' mechanism mediated by eIF2 facilitates the probing of start codons by the initiator tRNA.
• This study provides structural insights into the dynamic role of eIF2 in ensuring accurate translation initiation.