HP1 holin family
The HP1 Holin Family is a member of the Holin Superfamily II. Proteins in this family are typically found to contain two transmembrane segments and range between 70 and 80 amino acyl residues in length. A representative list of proteins belonging to the HP1 holin family can be found in the .
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 transmembrane segments 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.