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Applied and Environmental Microbiology, December 2005, p. 8744-8751, Vol. 71, No. 12
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.12.8744-8751.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Institute of Marine Biology, National Taiwan Ocean University, Keelung 20224, Taiwan, Republic of China,1 Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei 11529, Taiwan, Republic of China2
Received 18 April 2005/ Accepted 10 August 2005
A novel death-specific gene, ScDSP, was obtained from a death stage subtraction cDNA library of the diatom Skeletonema costatum. The full length of ScDSP cDNA was 921 bp in length, containing a 699-bp open reading frame encoding 232 amino acids and two stretches of 66 and 156 bp in the 5' and 3' untranslated regions, respectively. Analysis of the peptide structure revealed that ScDSP contained a signal peptide domain, a transmembrane domain, and a pair of EF-hand motifs. When S. costatum grew exponentially at a rate of 1.3 day1, the ScDSP mRNA level was at 2 µmol · mole 18S rRNA1. In contrast, when the culture entered the death phase with a growth rate decreasing to 0.5 day1, ScDSP mRNA increased dramatically to 668 µmol · mole 18S rRNA1, and a high degree of DNA fragmentation was simultaneously observed. Under the influence of a light-dark cycle, ScDSP expression in both exponential and stationary phases clearly showed a diel rhythm, but the daily mean mRNA level was significantly higher in the stationary phase. Our results suggest that ScDSP may play a role in the molecular mechanism of self-destructive autolysis in phytoplankton under stress.
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