His-Asn-His (HNH) proteins are a very common family of small nucleic acid-binding proteins that are generally associated with endonuclease activity [4].

1: Amino acid sequence motif of group I intron endonucleases is conserved in open reading frames of group II introns. Shub DA, Goodrich-Blair H, Eddy SR; Trends Biochem Sci 1994;19:402-404. PMID:7817395

2: Statistical modeling and analysis of the LAGLIDADG family of site-specific endonucleases and identification of an intein that encodes a site-specific endonuclease of the HNH family. Dalgaard JZ, Klar AJ, Moser MJ, Holley WR, Chatterjee A, Mian IS; Nucleic Acids Res 1997;25:4626-4638. PMID:9358175

3: Self-splicing group I and group II introns encode homologous (putative) DNA endonucleases of a new family. Gorbalenya AE; Protein Sci 1994;3:1117-1120. PMID:7920259

4: Biochemical characterization of a thermostable HNH endonuclease from deep-sea thermophilic bacteriophage GVE2. Zhang L, Huang Y, Xu D, Yang L, Qian K, Chang G, Gong Y, Zhou X, Ma K; Appl Microbiol Biotechnol. 2016;100:8003-8012. PMID:27131500