Introduction

NtcA is a global transcriptional regulator for nitrogen control present in every cyanobacteria tested (Herrero et al. 2001) and most of its targets are genes involved on nitrogen assimilation. Non-diazotrophic cyanobacteria degrade their light-harvesting antennae, the phycobilisomes, when exposed to a variety of stress conditions, including nitrogen starvation. This phenomenon, termed chlorosis or bleaching has been shown to be dependent of the response regulator NblR in Synechococcus sp. PCC 7942 (Schwarz, Grossman 1998). The expression of nblA, a key gene in degradation of phycobilisomes is induced during nitrogen starvation, although previous work failed to show the direct involvement of NtcA on nblA expression (Bhaya et al. 2000).

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