This is an alpha and beta fold domain [1]. It has a conserved aspartate, and an asparagine residue followed by a basic residue in a Nx+ motif [1]. This predicted structural domain is mainly found in polyvalent proteins of phages/prophages [1]. The P1 hdf protein, a solo version of the domain, and the Phage P1 DarA protein that contains this domain are components of the phage P1 head [1]. The domain might be involved in a counter-restriction activity [1].

1: Polyvalent Proteins, a Pervasive Theme in the Intergenomic Biological Conflicts of Bacteriophages and Conjugative Elements. Iyer LM, Burroughs AM, Anand S, de Souza RF, Aravind L; J Bacteriol. 2017; [Epub ahead of print] PMID:28559295