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P F Lin

Publications and source records attributed to P F Lin.

47 records · Page 3Linked to original sources
PubMed1982

Partial purification and characterization of the mRNA for human thymidine kinase and hypoxanthine/guanine phosphoribosyltransferase.

We used direct microinjection of poly(A)+RNA into individual hypoxanthine/guanine phosphoribosyltransferase-deficient or thymidine kinase-deficient cells and detected the specific in vivo translation products as an assay for human hypoxanthine/guanine phosphoribosyltransferase or thymidine kinase mRNAs. The incorporation of [3H]hypoxanthine or [3H]thymidine into cells in response to injected mRNA was assayed in situ by autoradiography. Methylmercuric hydroxide/agarose gel analysis showed that human hypoxanthine/guanine phosphoribosyltransferase mRNA contains approximately 1,530 nucleotides, which is twice the number required for its protein coding capacity. The mRNA for human cytoplasmic thymidine kinase is estimated to be approximately the same length; thus, the size of the cytosol thymidine kinase subunit can be predicted to be approximately 47,000 daltons, if the full coding capacity of its mRNA is utilized.

Biological Assay↗
PubMed1981

Murine DNA repair gene located on chromosome 4.

Xeroderma pigmentosum (XP) is an autosomal recessive human disease in which affected individuals are prone to develop skin cancers after exposure to sunlight. Cells from XP patients are defective in DNA repair activity and are sensitive to UV light. Most XP individuals have a defect in the excision repair pathway for UV damage. Genetic studies have indicated that excision-defective cells fall into seven complementation groups (A-G). An eighth group of XP is known to be defective in post-replication repair. DNA repair enzymes are ubiquitous and can function across species boundaries. Primary mouse embryo fibroblasts have normal levels of DNA repair functions. We report here that somatic cell hybrids between primary mouse cells and SV40-transformed XP group A cells can express wild-type levels of DNA repair function. These hybrid cells segregate murine chromosomes in culture. The proportion of cells in a given hybrid cell line which can perform unscheduled DNA synthesis (UDS) correlated well with the percentage of the population retaining murine chromosome 4. This study presents the first example of a direct quantitative comparison of specific gene activity and chromosomal content on a cellular basis.

Animals↗
PubMed1980

Assignment of the murine interferon sensitivity and cytoplasmic superoxide dismutase genes to chromosome 16.

Both hybrids of mouse and human microcells and whole cell hybrids generated by the fusion of primary mouse cells and SV40-transformed human fibroblasts were used to establish the syntenic association of the murine cytoplasmic superoxide dismutase and the interferon sensitivity genes on mouse chromosome 16. This assignment adds two new markers to chromosome 16 and provides another example of an evolutionarily conserved linkage. This finding also provides an animal model both for cellular responsiveness to interferon and for Down's syndrome.

Animals↗
PubMed1979

Genetic control of cobalamin binding in normal and mutant cells: assignment of the gene for 5-methyltetrahydrofolate:L-homocysteine S-methyltransferase to human chromosome 1.

When extracts prepared from cultured human or rodent fibroblasts grown in medium containing [(57)Co]cobalamin were analyzed by polyacrylamide gel electrophoresis, most of the intracellular radioactivity migrated with the activity of the cobalamin-dependent enzyme 5-methyltetrahydrofolate:L-homocysteine S-methyltransferase (EC 2.1.1.13). Because the rodent and human forms of this enzyme are electrophoretically different, we used the binding of [(57)Co]cobalamin to detect the presence of the human methyltransferase isozyme in rodent-human somatic cell hybrids. As expected, binding and methyltransferase activities were found to cosegregate, thus confirming genetically their electrophoretic identity. Accordingly, we examined the [(57)Co]cobalamin-binding patterns and human chromosome contents of a panel of 12 rodent-human hybrid clones, and concluded that the gene for the methyltransferase (designated Mtr) is located on human chromosome 1. Using this information, we probed the nature of the molecular defect exhibited by fibroblasts cultured from patients expressing the cbl C mutation. Although these cells are unable to associate newly taken up [(57)Co]cobalamin with the methyltransferase, hybrids of mouse L-cells and cbl C cells containing chromosome 1 show a "reappearance" of the human [(57)Co]cobalamin-methyltransferase. These results indicate that the cbl C mutation does not affect the methyltransferase apoprotein, but rather some metabolic step that must convert cobalamin to a chemical form capable of attaching to the enzyme.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1977

Initiation of genetic exchanges in lambda phage--prophage crosses.

When Escherichia coli K-12 (lambda) lysogens were infected with lambda phages, genetic exchanges between phage and prophage occurred at low frequencies (less than 0.1% between the markers P3 and P80), but at frequencies above 1% if the infecting phages were first treated with the photosensitizing agent 4,5',8-trimethylpsoralen and 360 nm light. Exchanges were induced by psoralen damage at about the same frequency in wild-type lysogens and in those carrying recB(-), recC(-), recF(-), or lexA(-), but at an intermediate frequency in a quadruple mutant carrying recB(-)recC(-)recF(-)sbcB(-). Few if any exchanges were induced in lysogens carrying uvrA(-), uvrB(-), or recA(-). The increase in the frequency of recombination was presumably due to the psoralen damage in the phage DNA molecules and the action of host cell repair and recombination enzymes. The production of crosslinks in the phage DNA by psoralen and 360 nm light was measured by sedimentation in alkali. It showed second-order kinetics indicative of a two-photon reaction. In contrast, first-order kinetics had been reported for monoadduct formation. Second-order kinetics, similar to those for crosslink production, were found for genetic exchanges in homoimmune crosses. Presumably, crosslinks, rather than monoadducts, cause most of the exchanges. Because the uvrA(-) gene product (UV-endonuclease) was required, it is likely that recombination was initiated by DNA molecules cut at crosslinks. This system has been used to show that after the crosslinked phage duplex has been cut, one or more of the subsequent steps-homologous pairing, cutting, and joining-require the recA(+) gene product.

Coliphages↗
PubMed1976

Genetic exchanges caused by ultraviolet photoproducts in phage lambda DNA molecules: the role of DNA replication.

Genetic recombination induced by structural damage in DNA molecules was investigated in E. coli K12 (lambda) lysogens infected with genetically marked phage lambda. Photoproducts were induced in the phage DNA before infection by exposing them either to 313 nm light in the presence of acetophenone or to 254 nm light. To test the role of the replication of the damaged phage DNA on the frequency of the induced recombination, both heteroimmune and homimmune crosses were performed. First, samples of a heteroimmune phage lambda imm434 P80 exposed to these treatments were allowed to infect cells lysogenic for prophage lambda cI857 P3. Phage DNA replication and maturation took place, and the resulting progeny phages were assayed for the frequency of P+ recombinants. Recombination was less frequent in infected cells exposed to visible light and in wild type cells able to perform excision repair than in excision-defective lysogens. Therefore, much of the induced recombination can be attributed to the pyrimidine dimers in the phage DNA, the only photoproducts known to be dissociated by photoreactivating enzyme. Second, in homoimmune crosses, samples of similarly treated homoimmune lambda P3 phages were allowed to infect lysogens carrying lambda cI857 P80. Replication of the phage DNA containing ultraviolet photoproducts was repressed by lambda immunity, and was further blocked by the lack of the P gene product needed for replication. The lysogens were purified and scored for both colony forming ability and for P+ recombinant prophages. The 254 nm photoproducts increased the frequency of recombination in these homimmune crosses, even though phage DNA replication was blocked. Irradiation with 313 nm light and acetophenone M, which produces dimers and unknown photoproducts, was not as effective per dimer as the 254 nm light. It is concluded from these results that certain unidentified 254 nm photoproducts can cause recombination even in the absence of DNA replication. They are not pyrimidine dimers, as they are not susceptible to excision repair or photoreactivation. In contrast, pyrimidine dimers appear to cause recombination only when the DNA containing them undergoes replication.

Coliphages↗
PubMed1975

Genetic exchanges induced by structural damage in nonreplicating phage lambda DNA.

Genetic recombination between irradiated lambda phage and the unirradiated lambda prophage in homoimmune lysogens has been studied under conditions in which phage DNA replication and repair were controlled. The lambda phage were exposed to one of three treatments before infecting the lysogens: (a) 254-nm light, which produces pyrimidine dimers and other photoproducts; (b) 313-nm light with acetopheneone D, which produces thymine dimers and a different spectrum of other photoproducts; (c) 360-nm light with trimethylpsoralen, which produces monoadducts and cross-links. With both replication and excision-repair of the damaged phage DNA blocked, treatment b (acetophenone D) caused no significant increase in recombination, indicating that thymine dimers do not cause recombination if the DNA in which they are contained is not replicated. Treatment a (254 nm), producing the same total number of pyrimidine dimers, caused a marked increase in recombination. This indicates that photoproducts other than pyrimidine dimers produced by 254-nm light can cause recombination in the absence of replication. Treatment c (psoralen) caused a marked increase in recombination in wild type but not in uvrA and uvrB mutants. The frequency of recombination in two-factor crosses varied with marker separation in such a way as to suggest that cross-links can act over distances of at least 5% of the lambda genome to cause exchanges between pairs of relatively closely spaced markers. The psoralen photo cross-links and monoadducts initiate recombination only following the action of excision enzymes, which appears to release one arm of each cross-link, producing a gap with free strand ends. It may be these strand ends which induce recombination. The action at a distance of 5% of the lambda genome may reflect heteroduplex formation and the subsequent reduction to homozygosity of mismatched base pairs at genetic markers. Recombination between closely spaced markers in the P gene is reduced in strains carrying polA.

Coliphages↗
PubMedDate not supplied

Modulation of differentiation-related responses in human colon carcinoma cells by protein kinase inhibitor H-7.

1-(isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), a potent inhibitor of protein kinases, has been used as a tool to examine the role of protein kinases in a variety of cellular functions. Contingent on the cell type, H-7 has been reported either to inhibit or to promote differentiation. The biological effects of H-7 on human colon adenocarcinoma cells have not been reported. In this study we investigated the effects of H-7 on differentiation - related parameters such as cellular morphology, proliferation, the expression of carcinoembryonic antigen (CEA), fibronectin and cytokeratins in human adenocarcinoma cell lines HCT116 and SW480. H-7 induced pronounced morphological alterations in both cell lines. It induced fibronectin expression and down-modulated CEA expression and secretion in the SW480 cells, but not in the HCT116 cells. Expression of acidic keratins was not affected by H-7 treatment in both cell lines. However, the expression of basic keratins were down-modulated in the HCT116 cells and enhanced in the SW480 cells. These studies showed that the protein kinase inhibitor, H-7, modulated phenotypic properties in human colon adenocarcinoma cells. Alterations in phenotypic properties and their significance in regard to the induction of differentiation are discussed.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗