Ribonuclease D is a bacterial 3'-5' exonuclease that acts on tRNA. It contributes to the 3' maturation of several stable RNAs [1]. It consists of a catalytic domain (Pfam:PF01612) and two alpha- helical domains at the C-terminal that closely resemble the HRDC domain seen in RecQ-family helicases. This is the second HRDC domain from RNAse D. The first one is included in Pfam:PF00570.

1: Crystal structure of Escherichia coli RNase D, an exoribonuclease involved in structured RNA processing. Zuo Y, Wang Y, Malhotra A; Structure. 2005;13:973-984. PMID:16004870