1.E.20 The Pseudomonas aeruginosa Hol Holin (Hol Holin) Family

The hol gene (PRF9) product (117 aas) of Pseudomonas aeruginosa PAO1 exhibits a hydrophobicity profile similar to holins of P2 and φCTX phages with two peaks of hydrophobicity that might correspond to either one or two TMSs. Hol functions in conjunction with the lytic enzyme, Lys (PRF24; BAA83168, 209 aas). Hol by itself, when expressed in a broad host-range expression vector under IPTG control exhibited strong lytic activity in both P. aeruginosa and E. coli. Expression of the lys gene plus chloroform (but not minus chloramphenicol) yielded cell lysis. In another expression vector, coexpression of hol and lys induced lysis under conditions where neither gene alone induced lysis (Nakayama et al., 2000). The hol-lys gene system therefore is believed to constitute a chromosomally-encoded autolysis system.

The reaction probably catalyzed by Hol is:

Autolysin (Lys)in → Autolysin (Lys)out

This family belongs to the Holin III Superfamily .



Nakayama, K., K. Takashima, H. Ishihara, T. Shinomiya, M. Kageyama, S. Kanaya, M. Ohnishi, T. Murata, H. Mori, and T. Hayashi. (2000). The R-type pyocin of Pseudomonas aeruginosa is related to P2 phage, and the F-type is related to lambda phage. Mol. Microbiol. 38: 213-231.

Wang, D., J.M. Yu, R.J. Dorosky, L.S. Pierson, 3rd, and E.A. Pierson. (2016). The Phenazine 2-Hydroxy-Phenazine-1-Carboxylic Acid Promotes Extracellular DNA Release and Has Broad Transcriptomic Consequences in Pseudomonas chlororaphis 30-84. PLoS One 11: e0148003.


TC#NameOrganismal TypeExample

Holin, Hol (Nakayama et al. 2000)


Hol of Pseudomonas aeruginosa PAO1


Pyocin R2_PP holin


Pyocin R2-PP holin of Pseudomonas aeruginosa


SH3 type 3 domain-containing protein


SHE type 3 domain-containing protein of Brucella sp.


Holin of 115 aas and 3 TMSs, pyocin R2 holin.  Functions in DNA release within biofilms (Wang et al. 2016).  A gene cluster encoding a bacteriophage-derived pyocin and its lysis cassette was upregulated in phenozine producing strains. A holin encoded in this gene cluster was found to contribute to the release of eDNA in biofilm matrices, demonstrating that the influence of the phenozine, 2-OH-PCA, on eDNA production is due in part to cell autolysis as a result of pyocin production and release (Wang et al. 2016).

Holin of Pseudomonas chlororaphis


Uncharacterized protein of 104 aas and 2 or 3 TMSs

UP of Candidatus Pacearchaeota archaeon


Uncharacterized protein of 104 aas and 3 TMSs.

UP of Methanofollis liminatans