{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T16:59:27Z","timestamp":1791219567135,"version":"4.1.0"},"reference-count":45,"publisher":"Microbiology Society","issue":"10","license":[{"start":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T00:00:00Z","timestamp":1791158400000},"content-version":"unspecified","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Cystic Fibrosis Trust","award":["SRC017"],"award-info":[{"award-number":["SRC017"]}],"id":[{"id":"https:\/\/ror.org\/03xeae684","id-type":"ROR","asserted-by":"crossref"}]},{"name":"Philips","award":["N\/A"],"award-info":[{"award-number":["N\/A"]}],"id":[{"id":"https:\/\/ror.org\/02p2bgp27","id-type":"ROR","asserted-by":"crossref"}]},{"name":"Cambridge Trust","award":["N\/A"],"award-info":[{"award-number":["N\/A"]}]},{"name":"Medical Research Council"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,10,5]]},"abstract":"<jats:p>\n                    In this work, we show how exploration of genomic sequence space yields an unexpected evolutionary \u2018fix\u2019 that allows the cell to bypass the phenotypic defects associated with a dysfunctional enzyme. We identified a transposon (Tn) insertion in the gene (\n                    <jats:italic>argA<\/jats:italic>\n                    ) encoding\n                    <jats:italic>N<\/jats:italic>\n                    -acetylglutamate synthase (NAGS) that leads to arginine auxotrophy in\n                    <jats:italic>Pseudomonas aeruginosa<\/jats:italic>\n                    . This Tn insertion generates a truncated version of the ArgA protein (ArgA\n                    <jats:sub>188-432<\/jats:sub>\n                    ) that retains NAGS activity but, unlike the wild-type protein, is unrestrained by arginine feedback inhibition. However, the Tn::\n                    <jats:italic>argA<\/jats:italic>\n                    mutant readily re-acquired a prototrophic phenotype through the acquisition of spontaneous secondary mutations outside of the\n                    <jats:italic>argA<\/jats:italic>\n                    locus. Whole-genome sequencing and complementation analyses of one such \u2018bypass mutant\u2019 allowed us to trace this epistatic effect to an Ala128\u2192Val substitution in AmbA, a LysE-type transmembrane transporter. Using a variety of genetic approaches, we show that the\n                    <jats:italic>ambA<\/jats:italic>\n                    <jats:sup>Ala128Val<\/jats:sup>\n                    mutation gives rise to a change\/expansion of function in the encoded gene product and that this mutation is directly or indirectly responsible for bypassing the auxotrophy associated with the original Tn::\n                    <jats:italic>argA<\/jats:italic>\n                    mutation. Further analysis of the Tn::\n                    <jats:italic>argA ambA<\/jats:italic>\n                    <jats:sup>Ala128Val<\/jats:sup>\n                    mutant revealed that, compared with the \u2018wild-type\u2019 progenitor, the mutant exhibited large-scale changes in its proteome and metabolome consistent with elevated intracellular arginine and enhanced polyamine degradation. We conclude that the\n                    <jats:italic>ambA<\/jats:italic>\n                    <jats:sup>Ala128Val<\/jats:sup>\n                    mutation overcomes the phenotypic impact of the dysregulated ArgA\n                    <jats:sub>188-432<\/jats:sub>\n                    enzyme, possibly by enabling efflux of toxic polyamines (which we also show can competitively inhibit NAGS).\n                  <\/jats:p>","DOI":"10.1099\/mic.0.001760","type":"journal-article","created":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T16:16:54Z","timestamp":1791217014000},"source":"Crossref","is-referenced-by-count":0,"title":["An extragenic fix for a broken enzyme"],"prefix":"10.1099","volume":"172","author":[{"given":"Veena","family":"Mohan","sequence":"first","affiliation":[{"name":"Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK"},{"name":"Department of Biochemistry (Hopkins Building), University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Edoardo","family":"Labrini","sequence":"additional","affiliation":[{"name":"Department of Biochemistry (Hopkins Building), University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Cemile Selin","family":"Aksoy","sequence":"additional","affiliation":[{"name":"Biomedical Device Technology Program, Vocational School of Health Services, Izmir Democracy University, 35290, Izmir, Turkey"},{"name":"Department of Biochemistry (Hopkins Building), University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Volker","family":"Behrends","sequence":"additional","affiliation":[{"name":"School of Medicine and Biosciences, University of West London, St. Marys Road, London, W5 5RF, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Laila 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