Universal RNA-degrading enzymes in Archaea: Prevalence, activities and functions of β-CASP ribonucleases

β-CASP ribonucleases are widespread in all three domains of life. They catalyse both 5'-3' exoribonucleolytic RNA trimming and/or endoribonucleolytic RNA cleavage using a unique active site coordinated by two zinc ions. These fascinating enzymes have a key role in 3' end processing in Eukarya and in RNA decay and ribosomal RNA maturation in Bacteria. The recent recognition of β-CASP ribonucleases as major players in Archaea is an important contribution towards identifying RNA-degrading enzymes in the third domain of life. Three β-CASP orthologous groups, aCPSF1, aCPSF2, aCPSF1b, are closely related to the eukaryal CPSF73 termination factor and one, aRNase J, is ortholog of the bacterial RNase J. The endo- and 5'-3' exoribonucleolytic activities carried by archaeal β-CASP enzymes are strictly conserved throughout archaeal phylogeny suggesting essential roles in maturation and/or degradation of RNA. The recent progress in understanding the prevalence, activities and functions of archaeal β-CASP ribonucleases is the focus of this review. The current status of our understanding of RNA processing pathways in Archaea is covered in light of this new knowledge on β-CASP ribonucleases.