the bacteria R-M system as a model for devising human anti-viral gene or genomic vaccines and therapies since the RM system serves an innate defense-role in bacteria by restricting tropism by bacteriophages. There is research on REases and ZFN that can cleave the DNA of various human viruses, including HSV-2, high-risk HPVs and HIV-1, with the ultimate goal of inducing target mutagenesis and aberrations of human-infecting viruses. The human genome already contains remnants of retroviral genomes that have been inactivated and harnessed for self-gain. Indeed, the mechanisms for silencing active L1 genomic retroelements by the three prime repair exonuclease 1 (TREX1) and excision repair cross complementing 1(ERCC) appear to mimic the action of RM-systems in bacteria, and the non-homologous end-joining (NHEJ) that follows the use of ZFN without a repair template. Examples Examples of restriction enzymes include: Key: * = blunt ends N = C or G or T or A W = A or T See also BglII – a restriction enzyme EcoRI – a restriction enzyme HindIII – a restriction enzyme Homing endonuclease List of homing endonuclease cutting sites List of restriction enzyme cutting sites Molecular-weight size marker REBASE (database) Star activity References External links Molecular biology Biotechnology EC 3.1 Life sciences industry