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J. Biol. Chem., Vol. 276, Issue 27, 25088-25095, July 6, 2001

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A Novel Heat Shock Protein Plays an Important Role in Thermal Stress Management in Cyanobacteria^*

Hitoshi Nakamoto, Naoki Tanaka^§, and Natsuko Ishikawa

From the Department of Biochemistry and Molecular Biology, Saitama University, Urawa 338-8570, Japan

A novel heat shock gene, orf7.5, which encodes a putative acidic polypeptide of 63 amino acids, was cloned from the cyanobacterium Synechococcus sp. PCC 7942. Northern blot analysis revealed the presence of 400- and 330-base orf7.5 mRNAs, which were barely detectable in the cells grown at 30 °C but increased transiently in response to heat shock at 40 or 45 °C. Primer extension analysis showed that the two mRNAs have different 5'-ends. Chloramphenicol enhanced the accumulation of the orf7.5 mRNA, whereas it inhibited the increase in the amount of the groESL mRNA. To reveal the role of the orf7.5 gene in thermal stress management, we constructed a stable mutant in which a gene conferring resistance to an antibiotic was inserted into the coding region of the orf7.5 gene. The interruption led to a marked inhibition of growth at 45 °C and a decrease in the basal and acquired thermo-tolerances at 50 °C in the transformants, indicating that the gene plays a role in thermal stress management. The orf7.5 mutant could be complemented with a return to the wild type phenotype by a DNA fragment containing orf7.5 but not by mutated orf7.5s, in which a nonsense mutation was generated by introducing a frameshift or a point mutation within the orf7.5-coding region. Thus, thermo-tolerance requires an appropriate translation product, not simply a transcript. Accumulation of the groESL transcript in the orf7.5 mutant was strongly reduced, suggesting that the orf7.5 gene product controls the expression of the groESL operon.

The nucleotide sequence reported in this paper has been submitted to the DDBJ/GenBank^TM/EBI Data Bank with accession number AB002694.

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