Enterobacteria satellite phage P4 gene beta (P13057, 354 aa, ~39.9 kDa) is located in the left-end nonessential region of the P4 genome (gop-beta-cII gene cluster) [PMID:2403440, PMID:2183201].
gop and beta are cotranscribed rightward from the same promoter, and that the gop gene product is lethal to Escherichia coli when functional Beta protein is absent (beta mutants such as betaam1 or temperature-sensitive betats) [PMID:2403440, "The newly sequenced region encodes three nonessential genes, which are called gop, beta, and cII (in order, from left to right). The gop gene product kills Escherichia coli when the beta protein is absent; the gop and beta genes are transcribed rightward from the same promoter."].Pfam:PF14350 (Beta_protein) / InterPro:IPR025683 (Protein_beta), and together with Gop forms an anti-phage defense / toxin-antitoxin-like module in the P4 prophage lifestyle. However, its direct enzymatic substrate or biochemical mode of Gop neutralization has not been experimentally defined in the cached literature PMID:2403440.existing_annotations and core_functions are therefore left empty pending experimental characterization.