Beschreibung:
<jats:p><jats:bold>ABSTRACT. </jats:bold> The bacterium <jats:italic>Holospora oblusa</jats:italic> is a macronuclear‐specific symbiont of the ciliate <jats:italic>Paramecium caudatum. H. obtusa</jats:italic>‐bearing paramecia could survive even after the cells were quickly heated from 25°C to 35°C. To determine whether infection with <jats:italic>H. obtusa</jats:italic> confers heat shock resistance on its host, we isolated genes homologous to the heat shock protein genes hsp60 and hsp70 from <jats:italic>P. caudatum</jats:italic>. The deduced amino acid sequences of both cDNAs were highly homologous to hsp family sequences from other eukaryotes. Competitive PCR showed that <jats:italic>H. obtusa</jats:italic>‐free paramecia expressed only trace amounts of hsp60 and hspVO mRNA at 25°C, but that expression of hsp70 was enhanced immediately after the cells were transferred to 35°C. <jats:italic>H. obtusa</jats:italic>‐bearing paramecia expressed high levels of hsp70 mRNA even at 25°C and the level was further enhanced when the cells were incubated at 35°C. In contrast, the expression pattern of hsp60 mRNA was the same in <jats:italic>H. obtusa</jats:italic>‐bearing as in <jats:italic>H. obtusa</jats:italic>‐freeparamecia. These results indicate that infection with its endosymbiont can confer a heat‐shock resistant nature on its host cells.</jats:p>