1.E.7 The HP1 Holin (HP1 Holin) Family

See 1.E for a generalized description of Holins.

The NucE protein in Serratia marcescens shows homology to phage holin proteins involved in releasing lysozyme to the peptidoglycan of Gram-negative bacteria. The protein contains two characteristic TMSs with a positively charged C-terminus. When the nucC operon carrying the nucEDC genes is placed in the Escherichia coli chromosome, NucE functions as a holin. Additionally, NucE can complement lysis-defective bacteriophage mutants to allow for plaque formation and release of phage. Although NucE can function as a holin it is not involved in the transport of nuclease, an extracellular protein encoded by the nucA gene.

The proteins of 1.E.7 show some sequence similarity with those of family 1.E.1

This family belongs to the Holin Superfamily II.



Berkmen, M., M.J. Benedik, and U. Bläsi. (1997). The Serratia marcescens NucE protein functions as a holin in Escherichia coli. J. Bacteriol. 179: 6522-6524.

Jin, S., Y. Chen, G.E. Christie and M.J. Benedik (1996). Regulation of the Serratia marcescens extracellular nuclease: positive control by a homolog of P2 Ogr encoded by a cryptic prophage. J. Mol. Biol. 256: 264-278.

Strych U., W. Dai, and M.J. Benedik (1999). The NucE and NucD lysis proteins are not essential for secretion of the Serratia marcescens extracellular nuclease. Microbiology 145: 1209-1216.


TC#NameOrganismal TypeExample

Haemophilus influenzae phage HP1

Holin (78 aas; spP51727)


Holin of Haemophilus somnus


TC#NameOrganismal TypeExample

phage pg24 protein


gp24 of Burkholderia phage phi644-2