Involvement of the 5'-untranslated region in cold-regulated expression of the rbpA1 gene in the cyanobacterium Anabaena variabilis M3.

Transcript of the rbpA1 gene in Anabaena variabilis accumulates significantly at low growth temperatures below 28 degreesC. This accumulation was maximal at 16 degreesC. Accumulation of the rbpA1 transcript was completely abolished by rifampicin, but not by chloramphenicol. Photosynthesis was not required for this cold-induced accumulation. This accumulation of transcript was partly accounted for by increased stability of the rbpA1 transcript at low temperature. Expression of chimeric genes containing 3'-deleted rbpA1 sequences fused to the lacZ gene was regulated by low temperature when almost the entire 5'-untranslated region (5'-UTR) remained undeleted. Further deletion resulted in constitutive expression of the chimeric gene. The 5'-UTR sequence formed two types of complexes in vitro with protein extract from cells grown at 38 degreesC, but not with extract from the 22 degreesC grown cells. Affinity purification identified polypeptides of 75 and 32 kDa in Complex 1 and a 72 kDa polypeptide in Complex 2. These results are compatible with a model in which expression of the rbpA1 gene is regulated by transcriptional derepression at low temperature, although additional mechanisms, such as regulation of mRNA stability, might also contribute to temperature-dependent regulation.