The <em>rnb</em> Gene of <em>Synechocystis</em> PCC6803 Encodes a RNA Hydrolase Displaying RNase II and Not RNase R Enzymatic Properties

<div><p>Cyanobacteria are photosynthetic prokaryotic organisms that share characteristics with bacteria and chloroplasts regarding mRNA degradation. <em>Synechocystis sp.</em> PCC6803 is a model organism for cyanobacteria, but not much is known about the mechanism of RNA degradation. Only one member of the RNase II-family is present in the genome of <em>Synechocystis sp</em> PCC6803. This protein was shown to be essential for its viability, which indicates that it may have a crucial role in the metabolism of <em>Synechocystis</em> RNA. The aim of this work was to characterize the activity of the RNase II/R homologue present in <em>Synechocystis sp.</em> PCC6803. The results showed that as expected, it displayed hydrolytic activity and released nucleoside monophosphates. When compared to two <em>E. coli</em> counterparts, the activity assays showed that the <em>Synechocystis</em> protein displays RNase II, and not RNase R characteristics. This is the first reported case where when only one member of the RNase II/R family exists it displays RNase II and not RNase R characteristics.</p> </div>