DISRUPTION OF A SPE-LIKE OPEN READING FRAME ALTERS POLYAMINE CONTENT AND PSBA-2 MESSENGER-RNA STABILITY IN THE CYANOBACTERIUM SYNECHOCYSTISSP. PCC-6803

In Synechocystis 6803, transcripts of the psbA-2 gene encoding the rea ction-center protein D1 of photosystem II are short-lived in light but stable in darkness. No dark-stabilization was observed if the genomic region downstream from the psbA-2 gene was disrupted. The deleted fra gment was found to include an open reading frame (ORF) with striking s imilarity to the spe gene encoding arginine decarboxylase (L-arginine carboxy-lyase, EC 4.1.1.19), which is involved in the biosynthesis of polyamines. The spermidine content of the mutants with a disrupted ORF was observed to be lower than in the wild-type suggesting that polyam ines may play a role in the stability of the psbA-2 mRNA.