title: The role of IF-3 in the translation of T7- and phi80trp messenger RNA.
abstract: The DNA dependent synthesis of proteins was studied with a system composed of DNA, washed ribosomes, centrifuged (150,000 X g) bacterial extract from Escherichia coli and purified initiation factors IF-1 and IF-2. Synthesis of active enzymes encoded by the tryptophan (trp)-operon of E. coli was found to depend strongly on the addition of IF-3, with the same IF-3 dependency for all 5 gene-products of this operon, irrespective of the presence of the promotor proximal gene trpE. Synthesis of T7 RNA polymerase with T7 DNA as a template, however, was completely independent of the addition of IF-3. The same difference in IF-3 requirement was found when we compared the overall protein synthesis directed by these templates. This difference could be related to the effect of IF-3 on the formation of initiation complexes with the in vitro prepared mRNA: initiation complexes are readily formed with T7 mRNA also in the absence of IF-3, whereas the formation of these complexes with phi80trp mRNA almost completely depends on the presence of this factor.
mesh_terms: D003090:Coliphages; D004279:DNA, Viral; D004926:Escherichia coli / Q000378:metabolism; D009876:Operon; D010448:Peptide Initiation Factors; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D012367:RNA, Viral / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism; D013698:Templates, Genetic; D014158:Transcription, Genetic; D014364:Tryptophan / Q000378:metabolism; D014764:Viral Proteins / Q000096:biosynthesis*
chemical_list: D004279:DNA, Viral; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D012367:RNA, Viral; D014764:Viral Proteins; D014364:Tryptophan