It should be noted that in our experimental condition, there are a lot of intermediate products between 41-bp and 25-bp, also below 25-bp, especially in cell extract-mediated BER reaction , which is probably due to some nicks in the plasmid DNA. Also, we did not see much difference in LP and SN BER products between wild-type MEF and pol b 2/2 cell extract. This could be due to the incubating reactions too long and the substrate concentrations are below their Km. Much further optimization is needed for our in vitro BER assay to avoid these confounding factors. In summary, our work presents a major advance in the expression and assembling of human DNA pol d in infected silkworm larvae with a MK-2206 recombinant BmNPV virus in which the cDNAs for pol d four subunits were constructed into a single virus, each in an individual expression cassette. Highly purified recombinant pol d, as much as 4 mg heterotetramer from 350 larvae by a standardized protocol, is shown to be functional similar to those from natural sources by rigorous characterization and comparison of its activities and homogeneity. Also pol d plays a significant role by modulating the rate of SN BER and LP BER during the repair process through its conversion from heterotetrameric to trimeric form lacking p12. Pol d is a key enzyme in DNA replication and repair, and defects in pol d have been linked to genomic instability. Our research provides a simple novel method for the large scale preparation of human DNA pol d, which makes it feasible to study at the biochemical level various cellular processes which may lead to or prevent the development of cancer in human. A low tissue oxygen concentration, followed by the reintroduction of oxygen, gives rise to a SJN 2511 phenomenon known as ischemia/ reperfusion injury, and is central to the progression of numerous human pathologies . Current treatments are essentially limited to restoring blood flow to the affected region and therapy to diminish negative effects of the injury. Although cells have mechanisms to ameliorate the effects of resulting damage, the harmful intracellular conditions accompanying IR often override these defenses, causing necrotic or apoptotic cell death. This has particularly devastating consequences for tissues of limited regenerative ability, such as the brain and retina .