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The assimilation of all nitrogens from these purines indicates that the catabolic pathway is complete and proceeds past allantoin. Here we identify the genetic system responsible for the oxidation of hypoxanthine to allantoin in\n            <jats:italic>K. pneumoniae.<\/jats:italic>\n            The\n            <jats:italic>hpx<\/jats:italic>\n            cluster consists of seven genes, for which an organization in four transcriptional units,\n            <jats:italic>hpxDE<\/jats:italic>\n            ,\n            <jats:italic>hpxR<\/jats:italic>\n            ,\n            <jats:italic>hpxO<\/jats:italic>\n            , and\n            <jats:italic>hpxPQT<\/jats:italic>\n            , is proposed. The proteins involved in the oxidation of hypoxanthine (HpxDE) or uric acid (HpxO) did not display any similarity to other reported enzymes known to catalyze these reactions but instead are similar to oxygenases acting on aromatic compounds. Expression of the\n            <jats:italic>hpx<\/jats:italic>\n            system is activated by nitrogen limitation and by the presence of specific substrates, with\n            <jats:italic>hpxDE<\/jats:italic>\n            and\n            <jats:italic>hpxPQT<\/jats:italic>\n            controlled by both signals. Nitrogen control of\n            <jats:italic>hpxPQT<\/jats:italic>\n            transcription, which depends on \u03c3\n            <jats:sup>54<\/jats:sup>\n            , is mediated by the Ntr system. In contrast, neither NtrC nor the nitrogen assimilation control protein is involved in the nitrogen control of\n            <jats:italic>hpxDE<\/jats:italic>\n            , which is dependent on \u03c3\n            <jats:sup>70<\/jats:sup>\n            for transcription. Activation of these operons by the specific substrates is also mediated by different effectors and regulatory proteins. Induction of\n            <jats:italic>hpxPQT<\/jats:italic>\n            requires uric acid formation, whereas expression of\n            <jats:italic>hpxDE<\/jats:italic>\n            is induced by the presence of hypoxanthine through the regulatory protein HpxR. This LysR-type regulator binds to a TCTGC-N\n            <jats:sub>4<\/jats:sub>\n            -GCAAA site in the intergenic\n            <jats:italic>hpxD-hpxR<\/jats:italic>\n            region. When bound to this site for\n            <jats:italic>hpxDE<\/jats:italic>\n            activation, HpxR negatively controls its own transcription.\n          <\/jats:p>","DOI":"10.1128\/jb.01022-08","type":"journal-article","created":{"date-parts":[[2008,10,11]],"date-time":"2008-10-11T00:45:11Z","timestamp":1223685911000},"page":"7892-7903","update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":36,"title":["The\n            <i>hpx<\/i>\n            Genetic System for Hypoxanthine Assimilation as a Nitrogen Source in\n            <i>Klebsiella pneumoniae<\/i>\n            : Gene Organization and Transcriptional Regulation"],"prefix":"10.1128","volume":"190","author":[{"given":"Lucia","family":"de la Riva","sequence":"first","affiliation":[{"name":"Departament de Bioqui\u0301mica i Biologi\u0301a Molecular, Institut de Biomedicina de la Universitat de Barcelona, Facultat de Farmacia, Universitat de Barcelona, E-08028 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Josefa","family":"Badia","sequence":"additional","affiliation":[{"name":"Departament de Bioqui\u0301mica i Biologi\u0301a Molecular, Institut de Biomedicina de la Universitat de Barcelona, Facultat de Farmacia, Universitat de Barcelona, E-08028 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Juan","family":"Aguilar","sequence":"additional","affiliation":[{"name":"Departament de Bioqui\u0301mica i Biologi\u0301a Molecular, Institut de Biomedicina de la Universitat de Barcelona, Facultat de Farmacia, Universitat de Barcelona, E-08028 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Robert A.","family":"Bender","sequence":"additional","affiliation":[{"name":"Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Laura","family":"Baldoma","sequence":"additional","affiliation":[{"name":"Departament de Bioqui\u0301mica i Biologi\u0301a Molecular, Institut de Biomedicina de la Universitat de Barcelona, Facultat de Farmacia, Universitat de Barcelona, E-08028 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"235","reference":[{"key":"e_1_3_2_2_2","doi-asserted-by":"publisher","DOI":"10.1128\/jb.170.12.5588-5593.1988"},{"key":"e_1_3_2_3_2","first-page":"1001","volume":"120","year":"1977","unstructured":"Bender, R. 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