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J L Van Lancker

Publications and source records attributed to J L Van Lancker.

At least 19 recordsLinked to original sources
PubMed1981

Endonuclease activity on damaged DNA in rat regenerating liver.

The activity of an endonuclease(s) acting on double-stranded, ultraviolet-irradiated, and 2-acetylaminofluorene-bound DNA but not on double-stranded undamaged DNA triples within two hr after partial hepatectomy. Although the activity drops between four and six hr after operation, it remains above levels measured in livers of nonhepatectomized rats until 36 hr after operation. Between 36 and 48 hr after operation, the enzyme activity drops below the levels in liver of nonhepatectomized rats and then rises slowly to reach levels observed in nonhepatectomized animals between 48 hr and seven days after the operation. Studies on the effect of actinomycin on the activity of crude enzyme and on the incorporation of [14C]leucine and [14C]valine on the purified enzyme indicate that the increase in enzyme activity results from de novo synthesis. Eight % of endonucleolytic activity detectable in the crude homogenate is inhibited by an hyperimmune serum prepared against the purified enzyme. By adjusting the time of injection of 2-[14C]acetylaminofluorene with respect to the levels of enzyme activity after partial hepatectomy, an inverse correlation between binding and enzyme activity was demonstrated.

2-Acetylaminofluorene↗
PubMed1980

The action of a mammalian endonuclease on psoralen-bound DNA.

The sequential actions of two enzymes believed to be involved in DNA repair, namely a mammalian endonuclease and the bacterial DNA polymerase I on psoralen bound 32P-labeled DNA, was studied. When ultraviolet-irradiated DNA is exposed to the sequential action of the endonuclease, the formation of single-strand breaks prepares the DNA for the exonucleolytic excision of thymine dimers. The mammalian endonuclease purified from rat liver to electrophoretic homogeneity is inactive on normal DNA, DNA irradiated at 360 nm or DNA mixed with psoralen without irradiation. Incubation of psoralen-bound DNA labeled with 32P with the endonuclease releases the isotope in the acid soluble indicating that psoralen-bound DNA is susceptible to the endonucleolytic attack. Sedimentation of DNA on sucrose gradients indicates that there is no collapse of the DNA molecule after treatment with the endonuclease. Moreover, there is no release of the adduct in the acid soluble after treatment with DNA polymerase, indicating that the 5--3 min exonucleolytic activity of that enzyme is impaired by the remaining crosslinks. The crosslinks also inhibit the incorporation of [3H] dATP in presence of DNA polymerase I.

2-Acetylaminofluorene↗
PubMed1975

Alterations of liver DNA after x-irradiation. Reassociation and hybridization with nuclear RNA.

When RNA is extracted either from irradiated or unirradiated rat livers, no difference in its ability to hybridize with DNA is detectable. In contrast, the ability of DNA extracted from irradiated animals to hybirdize with RNA is decreased, probably as a result of DNA fragmentation. Sedimentation of X-irradiated DNA on sucrose gradients separates a small (low molecular weight) from a large peak (high molecular weight). The hybridization capacity for RNA of the large molecular weight DNA is similar to that of unirradiated DNA, but that of the small molecular weight is DNA reduced. After irradiation of the denatured DNA in vitro, the reassociation of DNA is inhibited, which suggests that DNA strands have lost part of their complementariness.

Animals↗