The addition of poly(A) tails to RNA is a phenomenon common to all organisms 
examined so far. No homologues of the known polyadenylating enzymes are found in 
Archaea and little is known concerning the mechanisms of messenger RNA 
degradation in these organisms. Hyperthermophiles of the genus Sulfolobus 
contain a protein complex with high similarity to the exosome, which is known to 
degrade RNA in eukaryotes. Halophilic Archaea, however, do not encode homologues 
of these eukaryotic exosome components. In this work, we analysed RNA 
polyadenylation and degradation in the archaea Sulfolobus solfataricus and 
Haloferax volcanii. No RNA polyadenylation was detected in the halophilic 
archaeon H. volcanii. However, RNA polynucleotidylation occurred in 
hyperthermophiles of the genus Sulfolobus and was mediated by the archaea 
exosome complex. Together, our results identify the first organism without RNA 
polyadenylation and show a polyadenylation activity of the archaea exosome.