Disruption Analysis of the Gene for a Cold-Regulated RNA-Binding Protein, rbpA1, in Anabaena: Cold-Induced Initiation of the Heterocyst Differentiation Pathway

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A cold-regulated operon, rbpA1-rpsU, encodes an RNA-binding protein and a ribosomal protein in Anabaena variabilis M3. The level of expression of this gene cluster was about ten times higher at temperatures below 30℃ than at 38℃. To study the role of the RbpA1 protein in vivo, we constructed insertional disruptants of rbpA1. These strains were totally devoid of RbpA1 protein but contained a normal level of the ribosomal protein S21, a product of the rpsU gene. The disruptants were morphologically normal at 38℃, but at 22℃ they produced unusual cells at a low frequency. These cells were probably at an ini-tial stage of proheterocyst formation. Various molecular events that are related to heterocyst initiation, namely, excision of the 11-kbp DNA element in nifD and the accumulation of transcripts of xisA and hetR, also occurred in the disruptants at 22℃ in the presence of nitrate ions, but these events did not occur in the presence of ammonium ions or at 38℃. The results suggest that RbpA1 is required for enhanced repression of heterocyst initiation at low temperatures in the presence of nitrate. Possible mechanisms of the action of RbpA1 are discussed.
日本植物生理学会の論文