Studies on the Role of Guanosine Triphosphate in Polypeptide Chain Initiation in Escherichia coli

摘要: Abstract 1. The formation and properties of the 30 S initiation complex its subsequent conversion to 70 have been studied. polypeptide chain contains fMet-tRNA intact GTP in equimolar amounts. Incorporation both species into requires mRNA (f2 RNA, poly (U, G), or A-U-G) large amounts factor IF 2. Initiation 1 stimulates formation. Addition 50 subunits isolated results hydrolysis all bound GDP Pi. In absence subunits, no occurs. Concurrently a couple is formed becomes available for peptidyl transfer. 3. Under appropriate conditions can be depleted complement while retaining full fMet-tRNA. released this manner remains intact. Such GTP-deficient still accept form donate fMet peptide linkage. 4. At low (catalytic) levels 2 necessary GTP-dependent using mixture ribosomal 5'-guanylyl methylene diphosphonate (GMP-PCP) does not replace GTP. high (stoichiometric) formation, GMP-PCP substitute promoting GMP-PCP-stimulated then subunit couple. However, inactive 5. A model process presented which suggests that translocation occur. Rather, it postulated binds directly donor site equivalent on subunit. Upon addition, formed. serves release from complex. Released recycles catalyze another round initiation. Release also "unblock"