This domain is the N-terminal region of the bacterial Hen1 protein. This protein forms stable hetero-tetramer with Pnkp. The hetero-tetramer was able to repair transfer RNAs cleaved by ribotoxins in vitro [1]. This domain provides the ligase activity of the hetero-tetramer.

1: Reconstituting bacterial RNA repair and modification in vitro. Chan CM, Zhou C, Huang RH; Science. 2009;326:247. PMID:19815768

2: Structural and biochemical insights into 2'-O-methylation at the 3'-terminal nucleotide of RNA by Hen1. Chan CM, Zhou C, Brunzelle JS, Huang RH; Proc Natl Acad Sci U S A. 2009; [Epub ahead of print] PMID:19822745