Translation initiation factor IF3: two domains, five functions, one mechanism?
Initiation factor IF3 contains two domains separated by a flexible linker. While the isolated N-domain displayed neither affinity for ribosomes nor a detectable function, the isolated C-domain, added in amounts compensating for its reduced affinity for 30S subunits, performed all activities of intact IF3, namely: (i) dissociation of 70S ribosomes; (ii) shift of 30S-bound mRNA from 'stand-by' to 'P-decoding' site; (iii) dissociation of 30S-poly(U)-NacPhe-tRNA pseudo- initiation complexes; (iv) dissociation of fMet-tRNA from initiation complexes containing mRNA with the non-canonical initiation triplet AUU (AUUmRNA); (v) stimulation of mRNA translation regardless of its start codon and inhibition of AUUmRNA translation at high IF3C/ribosome ratios. These results indicate that while IF3 performs all its functions through a C-domain-30S interaction, the N-domain function is to provide additional binding energy so that its fluctuating interaction with the 30S subunit can modulate the thermodynamic stability of the 30S-IF3 complex and IF3 recycling. The localization of IF3C far away from the decoding site and anticodon stem-loop of P-site-bound tRNA indicates that the IF3 fidelity function does not entail its direct contact with these structures.
Petrelli
D
D
Laboratory of Genetics, Department of Biology MCA, University of Camerino, I-62032 Camerino (MC), Italy.
LaTeana
A
A
Garofalo
C
C
Spurio
R
R
Pon
C L
CL
Gualerzi
C O
CO
D004926:Escherichia coli / Q000235:genetics; D039621:Eukaryotic Initiation Factor-3; D010448:Peptide Initiation Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger; D012358:RNA, Transfer, Met; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D012270:Ribosomes / Q000378:metabolism
D039621:Eukaryotic Initiation Factor-3; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D012358:RNA, Transfer, Met; D011993:Recombinant Fusion Proteins