This protein of approx. 100 residues is found in bacteria. It contains up to five alpha helices and up to seven beta strands and is probably monomeric. Its function is unknown. It is cited as a major prophage head protein [1], so might generally be of viral origin.

1: The prophages of Lactobacillus johnsonii NCC 533: comparative genomics and transcription analysis. Ventura M, Canchaya C, Pridmore RD, Brussow H; Virology. 2004;320:229-242. PMID:15016546