{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,19]],"date-time":"2025-10-19T18:12:54Z","timestamp":1760897574776},"reference-count":57,"publisher":"Wiley","issue":"2","license":[{"start":{"date-parts":[[2004,12,2]],"date-time":"2004-12-02T00:00:00Z","timestamp":1101945600000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecular Microbiology"],"published-print":{"date-parts":[[2005,1]]},"abstract":"<jats:title>Summary<\/jats:title><jats:p>DnaK and GroEL play a pivotal role in protein folding, and promote cell proliferation and survival. In Gram\u2010positive and several Gram\u2010negative bacteria, HrcA represses the transcription of<jats:italic>dnaK<\/jats:italic>and<jats:italic>groE<\/jats:italic>operons by binding to the highly conserved CIRCE (<jats:styled-content>c<\/jats:styled-content>ontrolling<jats:styled-content>i<\/jats:styled-content>nverted<jats:styled-content>r<\/jats:styled-content>epeat of<jats:styled-content>c<\/jats:styled-content>haperone<jats:styled-content>e<\/jats:styled-content>xpression) operator sequence in the presence of GroEL. HrcA may respond to environmental stress and various other factors that modulate the transcription of the<jats:italic>dnaK<\/jats:italic>and<jats:italic>groE<\/jats:italic>operons. However, the mechanisms by which these factors modulate the activity of HrcA remain elusive. Here, we show that the thermoresistance of<jats:italic>Streptococcus pneumoniae<\/jats:italic>is significantly repressed in the presence of Ca<jats:sup>2+<\/jats:sup>. Furthermore, heat shock\u2010induced expression of the CIRCE regulon in<jats:italic>S. pneumoniae<\/jats:italic>is repressed in the presence of Ca<jats:sup>2+<\/jats:sup>, although to a lesser degree than in the<jats:italic>hrcA<\/jats:italic>mutant, strongly suggesting that HrcA inhibits expression of the CIRCE regulon in a Ca<jats:sup>2+<\/jats:sup>\u2010dependent manner. Although HrcA does not bind directly to Ca<jats:sup>2+<\/jats:sup>, its hydrophobicity is increased in the presence of the metal ion. Taken together, our observations suggest that Ca<jats:sup>2+<\/jats:sup>induces conformational changes, such as exposure of the hydrophobic surfaces of HrcA, which facilitate binding to GroEL. Alternatively, the presence of Ca<jats:sup>2+<\/jats:sup>may facilitate GroEL in interacting freely with HrcA. This, in turn, enhances access to CIRCE and leads to repression of the<jats:italic>dnaK<\/jats:italic>and<jats:italic>groE<\/jats:italic>operons in<jats:italic>S. pneumoniae<\/jats:italic>.<\/jats:p>","DOI":"10.1111\/j.1365-2958.2004.04416.x","type":"journal-article","created":{"date-parts":[[2005,1,28]],"date-time":"2005-01-28T16:39:49Z","timestamp":1106930389000},"page":"456-468","source":"Crossref","is-referenced-by-count":12,"title":["Ca<sup>2+<\/sup>\u2010dependent expression of the CIRCE regulon in<i>Streptococcus pneumoniae<\/i>"],"prefix":"10.1111","volume":"55","author":[{"given":"Hyog\u2010Young","family":"Kwon","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Su\u2010Nam","family":"Kim","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Suhk\u2010Neung","family":"Pyo","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Dong\u2010Kwon","family":"Rhee","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2004,12,2]]},"reference":[{"key":"e_1_2_7_2_1","doi-asserted-by":"publisher","DOI":"10.1128\/IAI.57.8.2324-2330.1989"},{"key":"e_1_2_7_3_1","doi-asserted-by":"publisher","DOI":"10.1074\/jbc.273.6.3257"},{"key":"e_1_2_7_4_1","doi-asserted-by":"publisher","DOI":"10.1126\/science.1970672"},{"key":"e_1_2_7_5_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-2958.1993.tb01727.x"},{"key":"e_1_2_7_6_1","doi-asserted-by":"publisher","DOI":"10.1146\/annurev.bi.56.070187.002143"},{"key":"e_1_2_7_7_1","doi-asserted-by":"publisher","DOI":"10.1128\/JB.183.24.7295-7307.2001"},{"key":"e_1_2_7_8_1","doi-asserted-by":"publisher","DOI":"10.1046\/j.1365-2958.2003.03355.x"},{"key":"e_1_2_7_9_1","doi-asserted-by":"publisher","DOI":"10.1042\/bj3010563"},{"key":"e_1_2_7_10_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-2958.2003.03892.x"},{"key":"e_1_2_7_11_1","doi-asserted-by":"publisher","DOI":"10.1038\/344789a0"},{"key":"e_1_2_7_12_1","doi-asserted-by":"publisher","DOI":"10.1128\/jb.172.12.6959-6972.1990"},{"key":"e_1_2_7_13_1","doi-asserted-by":"crossref","first-page":"1968","DOI":"10.1128\/iai.64.6.1968-1976.1996","article-title":"Elevated 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