text: Bacterial initiation factor 1 associates with the 30S ribosomal subunit in the A site and prevents an aminoacyl-tRNA from entering. It modulates IF2 binding to the ribosome by increasing its affinity. It may also prevent the 50S subunit from binding, stopping the formation of the 70S subunit. It also contains a β-domain fold common for nucleic acid-binding proteins. It is a homolog of eIF1A. Initiation factor IF-1 is the smallest translation factor at only 8.2kDa. Beyond blocking the A-site, it affects the dynamics of ribosome association and dissociation. IF-1 enhances dissociation with IF-3, likely by inducing conformational changes in the 30S subunit. It also increases the binding affinity of IF-2 to the 30S subunit, possibly by altering the subunit configuration. Though IF-1 occupies the A-site, it does so in a way that is distinct from tRNA binding. Structural studies show IF-1 inserts a loop into the minor groove of helix 44 of 16S rRNA, flipping out bases A1492 and A1493. This insertion repositions nucleotides of helix 44, transmitting a conformational change over a 70Å distance and rotating the head of the 30S subunit. IF-1 mutants can exhibit cold-sensitive phenotypes, indicating a role for the factor in cold shock adaptation. Certain mutations also lead to o of genes at low temperatures, suggesting IF-1 is involved in gene regulation. IF-1 actively modifies ribosome structure and dynamics during initiation, in addition to just blocking the A-site.