infA

infA is the gene that encodes translation initiation factor 1 (IF-1) in many bacteria and, in organelles such as chloroplasts, in their genomes. IF-1 is a small, basic protein of roughly 70–75 amino acids that participates in the initiation phase of protein synthesis. It binds to the 30S ribosomal subunit and helps regulate the assembly of the initiation complex, contributing to the proper placement of the initiator tRNA and preventing premature joining of the 50S subunit. IF-1 works in concert with other initiation factors, notably IF-2 and IF-3, to ensure accurate start codon recognition and efficient formation of the 70S initiation complex.

Distribution and evolution of infA vary across lineages. The gene is widespread among bacteria and also has homologs in chloroplasts and mitochondria. In some bacterial groups, infA is essential for viability, while in others its function can be compensated or the gene may be lost. In plant chloroplasts, infA is frequently transferred to the nuclear genome over evolutionary timescales, with the encoded product then imported into the organelle. The coding sequence is typically compact, reflecting the small size of the protein, and there is some variation in length and sequence among species.

Structure and genetics: infA is usually a single-copy gene located on the chromosome in bacteria, though genomic context can vary. The encoded IF-1 adopts a conserved fold common to initiation factors and shows limited but detectable sequence variation across taxa. Regulation of infA expression is linked to cellular growth conditions, as with many components of the translation apparatus.

See also: translation initiation factors IF-1, IF-2, IF-3; 30S ribosomal subunit; fMet-tRNA.