NEW STRUCTURAL PERSPECTIVES ON THE BACTERIAL INITIATION COMPLEX

Translation is the biological process that ultimately leads to the synthesis of a protein from the genetic material mRNA. Protein synthesis is essential for life as we know it, which is rooted in its extreme conservation throughout all living organisms. Translation is typically divided into four phases, the first of which, denominated translation initiation, is the most delicate step, as it entails the determining the correct start site of the produced protein. Previous structural studies allowed us to gain important insights into the position of translation Initiation Factors, and their function during the formation of the bacterial Initiation Complex and the proper positioning of the initiator tRNA on the start codon of the mRNA. Nevertheless, the limited resolution of the structures hampered gaining a pristine view of the molecular details that are essential for the correct assembly of this important step of translation. Moreover, little information is available regarding the differences underlying the initiation of translation on non-canonical start codons. Driven by recent improvements in cryo-EM, this work aims to fill these gaps and shed molecular insights into bacterial initiation of translation. This work further highlights for the first time, at molecular resolution, multiple important interactions that occurs between the 30S subunit, mRNA, initiator tRNA and initiation factors during the process of Initiation Complex formation. Supported by the structural data obtained, a new model for the order of initiation complex assembly is suggested. The model presented underlines the complexity of bacterial initiation of translation and paves the way for future experiments to gain a holistic view of this step of translation.