{'fraction_non_alphanumeric': 0.027603513174404015, 'fraction_numerical': 0.00878293601003764, 'mean_word_length': 5.071065989847716, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Interaction of bacterial initiation factor 2 with initiator tRNA.

Interaction of bacterial polypeptide chain initiation factor 2 (IF-2) with Escherichia coli formylmethionyl-tRNA in the absence of free Mg2+ renders the fMet-tRNA adsorable to nitrocellulose membrane filters. This reaction does not require GTP and is strongly inhibited by low concentration (1 mM) of Mg2+ in the reaction mixture. The structural requirements of the tRNA for binary complex formation have been studied using modified fMet-tRNAfMet molecules and a series of N-blocked and normal aminoacyl-rRNAs. It has been observed that IF-2 will not blind either to free formylmethionine or to a short fMet-oligonucleotide, but will bind to any xRNA structure covalently attached to an N-blocked methionine group. The E. coli initiator and noninitiator methiionine tRNAs, which have many differences in primary structure, were found to bind identically. In addition, fMet-tRNAfMet molecules containing structural modidifications at 20 different sites had the same affinity for IF-2 as unmodified fMet-tRNAfMet. N-blocked eukaryotic initiator tRNAs were also found to bind strongly to the factor. Binary complex formation was readily reversible, f[14C]Met-tRNAfMet being competed out by addition of an equal amount of unlabeled fMet-tRNAfMet to the preformed complex. In contrast, deacylated tRNAfMet was a poor compeitor, a 30-fold excess being required for 50% inhibition of complex formation in the presence of limiting factor. Although tRNAs having an N-blocked methionine were found to have the greatest affinity for IF-2, specificity for the amino acid in binary complex formation was not absolute. Partial binding was observed with N-substituted tyrosine, valine, and phenylalanine tRNAs, and weak or no binding with N-subsituted lysine, alanine, and leucine tRNAs. In all cases, N-blocked derivatives had a higher affinity for IF-2 than the corresponding unsubstituted aminoacyl-tRNAs. These results indicate that IF-2 alone is not capable of distinguishing the nucleotide sequence of tRNAs and selects the initiator tRNA by recognizing the fMet moiety. The overall data suggest that the role of IF-2 in formation of the ribosomal initiation complex is to stablize the interaction of fMet-tRNAfMet with the ribosome at low Mg2+ concentrations by binding to both the ribosomal particle and the fMet group of the tRNA.