eIF1

Eukaryotic initiation factor 1 (eIF1) is a small, conserved protein that participates in translation initiation in eukaryotes and in some archaea. It is a component of the 43S pre-initiation complex assembled on the 40S ribosomal subunit, together with other initiation factors such as eIF1A, eIF3, and the eIF2-GTP–Met-tRNAi complex. eIF1 helps regulate start codon selection and ribosome scanning, supporting the fidelity of initiation.

During mRNA scanning, eIF1 promotes an open, scanning-competent conformation of the 40S subunit and prevents premature recognition of non-initiator elements. This activity reduces initiation at non-optimal sites and helps ensure proper AUG start codon usage within a favorable context (often defined by surrounding Kozak sequences). When the initiator tRNAiMet base-pairs with the start codon, eIF1 dissociates from the complex, enabling a transition toward a closed conformation that facilitates downstream events, including recruitment of the 60S subunit to form the 80S initiation complex.

eIF1 interacts with multiple initiation factors, notably eIF1A and components of eIF3, and with the 40S subunit to exert its regulatory role. The protein is evolutionarily conserved across eukaryotes and in archaeal systems, reflecting a shared mechanism for start-site selection during translation initiation.

Defects in eIF1 function can disrupt translation fidelity and alter codon choice, and in many organisms eIF1 is essential for viability. Because of its central role in initiation fidelity, eIF1 is a focus of research into translational control and start codon recognition.