{'fraction_non_alphanumeric': 0.0473328324567994, 'fraction_numerical': 0.0405709992486852, 'mean_word_length': 5.466019417475728, '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}}
Discrimination between mono–and trimethylated cap structures by two isoforms of Caenorhabditis elegans eIF4E

Primitive eukaryotes like Caenorhabditis elegans produce mRNAs capped with either m7GTP or m32,2,7GTP. Caenorhabditis elegans also expresses five isoforms of the cap‐binding protein eIF4E. Some isoforms (e.g. IFE‐3) bind to m7GTP–Sepharose exclusively, whereas others (e.g. IFE‐5) bind to both m7GTP− and m32,2,7GTP–Sepharose. To examine specificity differences, we devised molecular models of the tertiary structures of IFE‐3 and IFE‐5, based on the known structure of mouse eIF4E‐1. We then substituted amino acid sequences of IFE‐5 with homologous sequences from IFE‐3. As few as two changes (N64Y/V65L) converted the cap specificity of IFE‐5 to essentially that of IFE‐3. Molecular dynamics simulations suggested that the width and depth of the cap‐binding cavity were larger in IFE‐5 than in IFE‐3 or the N64Y/V65L variant, supporting a model in which IFE‐3 discriminates against m32,2,7GTP by steric hindrance. Furthermore, the affinity of IFE‐5 (but not IFE‐3) for m32,2,7GTP was reversibly increased when thiol reagents were removed. This was correlated with the formation of a disulfide bond between Cys‐122 and Cys‐126. Thus, translation of m32,2,7GTP‐capped mRNAs may be regulated by intracellular redox state.