The Origin and Function of Cre Recombinase:

Bacteriophages can not reproduce sexually and therefore require a mechanism to parasitize host cells allowing them to insert their DNA and replicate themselves. The replication and insertion machinery can make mistakes and Cre recombinase is a protein that helps protect the integrety of the Bacteriophages genome. In the life cycle of Bacteriophage P1, the function of Cre recombinase is to maintain the bacteriophage genome as a monomeric, unit copy plasmid in the lysogenic state. The loxP site serves as a marker to assure that only one copy of the bacteriophage genome is present in the virus. If a second loxP site is present that indicates that there is more than one copy of the viral genome present. Cre recombinase will bind to the loxP sites thereby detecting the second copy of the genome and excises the DNA region between the two sequences. One half of each loxP site is excised leaving only one loxP site. Specifically, this mechanism is important to maintain correct DNA replication and cell division processes.