Structural domains comprising this superfamily share the structure of the epsilon, a new subunit of RNA polymerase (RNAP) found in Gram-Positive bacteria which bears remarkable similarity to the Gp2 family of phage proteins involved in the inhibition of host cell transcription following infection. Deletion of epsilon shows no phenotype and has no effect on the transcriptional profile of the cell. Determination of the location of epsilon within the assembly of RNA polymerase core by single-particle analysis suggests that it binds. Due to the structural similarity of epsilon with Gp2 and the fact they bind similar regions of RNA polymerase, toward the downstream side of the DNA binding cleft, we hypothesize that epsilon may serve a role in protection from phage infection PMID:25092033.