This is an alpha-helical domain that is usually N-terminal to a metallopeptidase domain [1]. The domain is found in both in polyvalent proteins of conjugative elements and phages/prophages [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