The expression of the rbp genes, which encode small RNA-binding proteins with a single RNA-recognition motif, is known to increase at low temperature in Anabaena variabilis M3. The 5′-untranslated region (UTR) of the rbpA1 gene is involved in the cold-regulation. We compared the regulation of the rbp genes in three strains of cyanobacteria having different temperature optima, namely, a mesophilic strain Anabaena sp. PCC 7120, a thermophilic strain Thermosynechococcus elongatus BP-1, and a psychrophilic Antarctic strain Oscillatoria sp. SU1. In Anabaena 7120 and T. elongatus, all the rbp gene sequences are known, and the 5′-UTR sequences of some rbp genes have a high similarity to the 5′-UTR of rbpA1. We found that transcripts as well as protein products of these rbp genes accumulated at low temperature. In addition, the expression of rbp genes increased at low temperature in the Oscillatoria sp. SU1. This suggests that a mechanism of cold-regulation of rbp genes is common among various species of cyanobacteria that belong to different taxa and have different temperature optima.
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