27Oct/060
TESTING TWO POSSIBLE FATHERS
If a child has two possible fathers and neither stands out as the likely biological father, DDC can perform a paternity test for both men. In fact, we encourage it to save you money. One paternity test with two alleged fathers costs less than two separate paternity tests. When two possible fathers participate in a paternity test, [...]27Oct/060
TENSION-DEPENDENT DNA CLEAVAGE BY RESTRICTION ENDONUCLEASES: TWO-SITE ENZYMES ARE “SWITCHED OFF” AT LOW FORCE
PNAS, Vol. 103, No. 31. (1 August 2006), pp. 11555-11560.DNA looping occurs in many important protein-DNA interactions, including those regulating replication, transcription, and recombination. Recent theoretical studies predict that tension of only a few piconewtons acting on DNA would almost completely inhibit DNA looping. Here, we study restriction endonucleases that require interaction at two separated sites for efficient cleavage. Using optical tweezers we measured the dependence of cleavage activity on DNA tension with 15 known or suspected two-site enzymes (BfiI, BpmI, BsgI, BspMI, Cfr9I, Cfr10I, Eco57I, EcoRII, FokI, HpaII, MboII, NarI, SacII, Sau3AI, and SgrAI) and six one-site enzymes (BamHI, EcoRI, EcoRV, HaeIII, HindIII, and DNaseI). All of the one-site enzymes were virtually unaffected by 5 pN of tension, whereas all of the two-site enzymes were completely inhibited. These enzymes thus constitute a remarkable example of a tension sensing "molecular switch." A detailed study of one enzyme, Sau3AI, indicated that the activity decreased exponentially with tension and the decrease was approx10-fold at 0.7 pN. At higher forces (approx20-40 pN) cleavage by the one-site enzymes EcoRV and HaeIII was partly inhibited and cleavage by HindIII was enhanced, whereas BamHI, EcoRI, and DNaseI were largely unaffected. These findings correlate with structural data showing that EcoRV bends DNA sharply, whereas BamHI, EcoRI, and DNaseI do not. Thus, DNA-directed enzyme activity involving either DNA looping or bending can be modulated by tension, a mechanism that could facilitate mechanosensory transduction in vivo. 10.1073/pnas.0604463103
20Oct/060
WHAT IF I DON?T NEED MY RESULTS FOR LEGAL PURPOSES?
Recently, one of our readers asked if our DNA testing services are only for people who need their test results for legal purposes (such as obtaining child support). The answer to this question is no, they are not. How you use your test results—for your own peace of mind or for legal purposes—is entirely up [...]13Oct/060
WHAT HAPPENS TO MY DNA AFTER TESTING?
Occasionally, our clients ask us, “What happens to my DNA after testing?” This blog entry answers that question and attempts to ease any concerns you may have about the use of your DNA samples or test results. DDC will only use your samples for the DNA testing needed to verify the family relationship you ask us [...]9Oct/060
