Prokaryotic initiation factor

Prokaryotes require the use of three initiation factors: IF1, IF2, and IF3, for translation.

IF1

IF1 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 .

IF2

IF2 binds to an initiator tRNA and controls the entry of that tRNA into the ribosome. IF2, bound to GTP, binds to the 30S P site. After associating with the 30S subunit, fMet-tRNA_f binds to the IF2 then IF2 transfers the tRNA into the partial P site. When the 50S subunit joins, it hydrolyzes GTP to GDP and P_i, causing a conformational change in the IF2 that causes IF2 to release and allow the 70S subunit to form.

IF3

IF3 is not universally found in all bacterial species but in E. coli it is required for the 30S subunit to bind to the initiation site in mRNA. In addition, it has several other jobs including stabilization of free 30S subunits, facilitation of 30S subunits binding to mRNA and checking for accuracy against the first aminoacyl-tRNA. It also allows for rapid codon-anticodon pairing for the initiator tRNA to bind quickly to. IF3 is required by the small subunit to form initiation complexes, but has to be released to allow the 50S subunit to bind.

External links

• Prokaryotic Initiation Factors at the US National Library of Medicine Medical Subject Headings (MeSH)