Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.1 (phosphodiesterase)
 18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The DNA synthesizing subunit (alpha-subunit) of DNA polymerase-alpha from calf thymus was separated from the other three subunits by immunoaffinity chromatography. The enzymatic properties of the alpha-subunit were characterized and compared with those of the four-subunit complex. Free alpha-subunit behaved in many respects like the four-subunit polymerase-primase. It was inhibited by aphidicolin and butylanilino-deoxyATP and catalyzed DNA synthesis on both gapped duplex DNA as well as primed single-stranded DNA with a preference of gapped DNA. The alpha-subunit is a quasi-processive enzyme with a processivity for about 9 nucleotides incorporated per single primer binding event. This is 2-fold lower than the processivity of the four-subunit complex. Despite this moderate processivity, free alpha-subunit was able to synthesize long stretches of DNA on singly primed natural psi X174am16 DNA. The accuracy of DNA synthesis of the free alpha-subunit was determined by using the psi X174am16 reversion assay to be 1 error per 50,000 nucleotides incorporated. An in vitro accuracy of 1 error in 54,000 nucleotides incorporated was measured in parallel for the four-subunit complex. Thus, the smaller subunits do not contribute to the overall accuracy of DNA polymerase-alpha. Consistent with this result is the observation that the polymerase to 3'----5'-exonuclease ratio was less than 1 to 2,500,000. Therefore, there is no evidence for the action of a cryptic proofreading activity with the alpha-subunit of DNA polymerase-alpha of mammalian origin.
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PMID:The DNA synthesizing subunit of polymerase-primase from calf thymus. 153 34

Hematoporphyrin derivative (HPD) plus photoradiation caused the inactivation of DNA polymerases from calf thymus and R3230AC rat mammary tumor. Photosensitization of purified DNA polymerase-alpha as well as two forms of DNA polymerase-delta (I and II) from calf thymus were evaluated. Although all polymerase enzyme forms were inactivated at 70 micrograms HPD/ml, DNA polymerase-delta II was the most sensitive, displaying a 90% inactivation under conditions that did not cause significant inactivation of the other polymerase forms. Unlike DNA polymerase-alpha, the delta-forms have an associated 3'- to 5'-exonuclease activity. The exonuclease associated with DNA polymerase-delta II was uniquely sensitive to a low level of HPD and light exposure. DNA polymerase-delta II can be distinguished from other polymerase forms in cell extracts by its relative insensitivity to the polymerase inhibitor N2-(p-n-butylphenyl)deoxyadenosine 5'-triphosphate. In cytosols prepared from calf thymus and R3230AC rat mammary tumors, DNA polymerase-delta II was preferentially inhibited by HPD plus light. Furthermore, in experiments in which tumor-bearing rats were administered HPD prior to preparation of tumor cytosols, DNA polymerase-delta II was specifically inactivated by exposure to light. These results are discussed in view of their possible role in cancer therapy, and the potential use of HPD as a specific inhibitory agent of DNA polymerase-delta II is suggested.
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PMID:Inhibition of mammalian DNA polymerases by hematoporphyrin derivative and photoradiation. 394 Jan 88