{'fraction_non_alphanumeric': 0.034511784511784514, 'fraction_numerical': 0.012626262626262626, 'mean_word_length': 4.91542288557214, '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}}
Better Is Not Always Best

Low-affinity nutrient transporters sense depletion earlier than high-affinity transporters, thus preparing cells for starvation. Once a cell has evolved a high-affinity transporter for nutrients like phosphate or zinc, why would it need to continue to make low-affinity transporters as well? Levy et al. address this question in yeast and show that the lower-affinity form does come in handy. When nutrients are plentiful, the low-affinity transporter is expressed and works fine. As nutrient concentrations are depleted, the low-affinity transporter begins to lose efficiency and the nutrient influx dips. This signals the cell to begin preparation for starvation—at a time earlier than it would have, if it had waited until nutrient concentrations got so low that function of the high-affinity transporter became compromised. Sensing a decrease in nutrient supply before concentrations get low enough to inhibit growth thus appears to be a key reason for expressing transporters of both low and high affinity. S. Levy, M. Kafri, M. Carmi, N. Barkai, The competitive advantage of a dual-transporter system. Science 334, 1408–1412 (2011). [Abstract] [Full Text]