This domain is found in Protein ea8.5 from Bacteriophage lambda and similar protein sequences mostly from tailed bacteriophages and bacterial prophages. It ranges from around 45 to 90 residues in length and is associated with nucleic acid binding function, playing an essential role in the inhibition of the initiation of DNA synthesis in the phage host. NMR analysis shows it adopts an homeodomain/zinc-finger fold, which suggests a regulatory role [1, 2, 3].

1: The solution structures of two prophage homologues of the bacteriophage lambda Ea8.5 protein reveal a newly discovered hybrid homeodomain/zinc-finger fold. Kwan JJ, Smirnova E, Khazai S, Evanics F, Maxwell KL, Donaldson LW; Biochemistry. 2013;52:3612-3614. PMID:23672713

2: The Role of the Exo-Xis Region in Oxidative Stress-Mediated Induction of Shiga Toxin-Converting Prophages. Licznerska K, Dydecka A, Bloch S, Topka G, Nejman-Falenczyk B, Wegrzyn A, Wegrzyn G; Oxid Med Cell Longev. 2016;2016:8453135. PMID:26798427

3: Ea22 Proteins from Lambda and Shiga Toxin-Producing Bacteriophages Balance Structural Diversity with Functional Similarity. Tong J, Nejman-Falenczyk B, Bloch S, Wegrzyn A, Wegrzyn G, Donaldson LW; ACS Omega. 2020;5:12236-12244. PMID:32548406