RNAse domain of the PIN fold [1] with an inserted Zinc Ribbon at the C terminus [2].

1: Comparative genomics and evolution of proteins involved in RNA metabolism. Anantharaman V, Koonin EV, Aravind L; Nucleic Acids Res. 2002;30:1427-1464. PMID:11917006

2: The prokaryotic antecedents of the ubiquitin-signaling system and the early evolution of ubiquitin-like beta-grasp domains. Iyer LM, Burroughs AM, Aravind L; Genome Biol. 2006;7:R60. PMID:16859499