1. Artemia encysted gastrulae have an enzyme which hydrolyzes 2':3' cyclic nucleotides monophosphate to give the corresponding nucleotides 2' phosphate. 2. The enzyme has different substrate specificity that the previously reported 2':3' cyclic nucleotide 3' phosphodiesterase (EC 3.1.4.37). 3. It hydrolyzes 2':3' cyclic guanosine monophosphate preferentially to the corresponding nucleotides of adenosine, cytidine and uridine. 4. An enzyme with the same catalytic characteristics, but differing in substrate specificity, is also present in the filamentous fungus Fusarium culmorum. 5. We could not find similar enzymatic activities in Escherichia coli, Saccharomyces cerevisiae or Drosophila. 6. The Artemia enzyme might be relevant in the modulation of the ribonuclease VI activity through generation of cytidine 2'-phosphate, a strong inhibitor of this ribonuclease.

This work was supported by a research grant (PB87-206) from the DGICYT, Promoción General del Conocimiento.

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