{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,10]],"date-time":"2026-06-10T16:40:43Z","timestamp":1781109643263,"version":"3.54.1"},"reference-count":50,"publisher":"National Academy of Sciences","issue":"12","content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[1997,6,10]]},"abstract":"<jats:p>\n                    <jats:italic>Rhizobium leguminosarum<\/jats:italic>\n                    bv. viciae expresses an uptake hydrogenase in symbiosis with peas (\n                    <jats:italic>Pisum sativum<\/jats:italic>\n                    ) but, unlike all other characterized hydrogen-oxidizing bacteria, cannot express it in free-living conditions. The hydrogenase-specific transcriptional activator gene\n                    <jats:italic>hoxA<\/jats:italic>\n                    described in other species was shown to have been inactivated in\n                    <jats:italic>R. leguminosarum<\/jats:italic>\n                    by accumulation of frameshift and deletion mutations. Symbiotic transcription of hydrogenase structural genes\n                    <jats:italic>hupSL<\/jats:italic>\n                    originates from a \u221224\/\u221212 type promoter (\n                    <jats:italic>hupS<\/jats:italic>\n                    <jats:sub>p<\/jats:sub>\n                    ). A regulatory region located in the \u2212173 to \u221288 region was essential for promoter activity in\n                    <jats:italic>R. leguminosarum<\/jats:italic>\n                    . Activation of\n                    <jats:italic>hupS<\/jats:italic>\n                    <jats:sub>p<\/jats:sub>\n                    was observed in\n                    <jats:italic>Klebsiella pneumoniae<\/jats:italic>\n                    and\n                    <jats:italic>Escherichia coli<\/jats:italic>\n                    cells expressing the\n                    <jats:italic>K. pneumoniae<\/jats:italic>\n                    nitrogen fixation regulator NifA, and in\n                    <jats:italic>E. coli<\/jats:italic>\n                    cells expressing\n                    <jats:italic>R. meliloti<\/jats:italic>\n                    NifA. This activation required direct interaction of NifA with the essential \u2212173 to \u221288 regulatory region. However, no sequences resembling known NifA-binding sites were found in or around this region. NifA-dependent activation was also observed in\n                    <jats:italic>R. etli<\/jats:italic>\n                    bean bacteroids. NifA-dependent\n                    <jats:italic>hupS<\/jats:italic>\n                    <jats:sub>p<\/jats:sub>\n                    activity in heterologous hosts was also absolutely dependent on the RpoN \u03c3-factor and on integration host factor. Proteins immunologically related to integration host factor were identified in\n                    <jats:italic>R. leguminosarum<\/jats:italic>\n                    . The data suggest that\n                    <jats:italic>hupS<\/jats:italic>\n                    <jats:sub>p<\/jats:sub>\n                    is structurally and functionally similar to nitrogen fixation promoters. The requirement to coordinate nitrogenase-dependent H\n                    <jats:sub>2<\/jats:sub>\n                    production and H\n                    <jats:sub>2<\/jats:sub>\n                    oxidation in nodules might be the reason for the loss of HoxA in\n                    <jats:italic>R. leguminosarum<\/jats:italic>\n                    and the concomitant NifA control of\n                    <jats:italic>hup<\/jats:italic>\n                    gene expression. This evolutionary acquired control would ensure regulated synthesis of uptake hydrogenase in the most common H\n                    <jats:sub>2<\/jats:sub>\n                    -rich environment for rhizobia, the legume nodule.\n                  <\/jats:p>","DOI":"10.1073\/pnas.94.12.6019","type":"journal-article","created":{"date-parts":[[2002,7,26]],"date-time":"2002-07-26T10:31:39Z","timestamp":1027679499000},"page":"6019-6024","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":61,"title":["Hydrogenase genes from\n                    <i>Rhizobium leguminosarum<\/i>\n                    bv. viciae are controlled by the nitrogen fixation regulatory protein\u2009NifA"],"prefix":"10.1073","volume":"94","author":[{"given":"Bel\u00e9n","family":"Brito","sequence":"first","affiliation":[{"name":"Laboratorio de Microbiolog\u00eda, Escuela T\u00e9cnica Superior Ingenieros Agr\u00f3nomos, Universidad Polit\u00e9cnica de Madrid, and Consejo 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