{'fraction_non_alphanumeric': 0.021152443471918306, 'fraction_numerical': 0.014587892049598834, 'mean_word_length': 5.381395348837209, '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}}
Light regulates the rate of translation elongation of chloroplast reaction center protein D1.

Intact and lysed chloroplasts isolated from the day or night phase of seedling growth exhibit a higher rate of [35S]Met incorporation into the D1 protein in the light than in darkness. In the presence of the translation initiation inhibitor lincomycin, radiolabel incorporation remains unaffected for 7.5-10 min of the in vitro translation reaction, indicating that radiolabel incorporation is regulated by translation elongation. The rate of [35S]Met incorporation into D1-protein can be increased by addition of exogenous ATP to the in vitro translation reactions; however, ATP cannot replace light, and at physiological concentrations of stromal ATP (40 microM), the rate is at least 25-fold higher in the light than in darkness. This indicates that translation elongation is arrested in darkness. Separation of translation-elongation reactions into polysome-bound and membrane-integrated D1 proteins demonstrates that the rate of translation elongation is higher in the presence of light. In the light, less time is required to transiently radiolabel a D1 translation intermediate of about 17 kDa and to chase the translation intermediate into mature D1 protein. We propose that light regulates the enzymatic activity of the translation-elongation process in chloroplasts.