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R Hand

Publications and source records attributed to R Hand.

70 records · Page 4Linked to original sources
PubMed1976

Thymidine metabolism and DNA synthesis in Newcastle disease virus-infected cells.

The inhibition of thymidine incorporation into DNA in Newcastle disease virus-infected cells has been studied. At 6 h after infection of L-929 cells at high multiplicity, transport of exogenous thymidine across the cell membrane was inhibited. The kinetics of this inhibition, decreased Vmax with no change in Km, suggest that there are fewer sites available for transport in infected cells. The conversion of thymidine to dTTP was not inhibited. Equilibrium of exogenous thymidine with the acid-soluble pool occurred more slowly and at a lower level of radioactivity than in uninfected cells, and there was a reduction in the rate of incorporation of exogenous thymidine into DNA. The reduction of incorporation into the pool and into DNA was proportionate. The size of total cellular dTTP pools was changed very little in infected cells. DNA synthesized in infected cells in the presence of [3H]BrdUrd had reduced incorporation of tritium but similar buoyant density to that from uninfected cells. The results show that Newcastle disease virus inhibits DNA synthesis directly and, in addition, decreases thymidine transport. Together these account for the overall decrease in thymidine incorporation into DNA of infected cells.

Biological Transport, Active↗
PubMed1975

A retarded rate of DNA chain growth in Bloom's syndrome.

The cytogenetic observation that homologous chromatid interchange occurs in Bloom's syndrome more often than normal prompted an investigation of DNA replication in that rare genetic disorder. Using DNA fiber autoradiography, an estimation was made of the rate of one component of ongoing DNA replication, DNA chain growth. The rate in Bloom's syndrome dermal fibroblasts in tissue culture was found to be significantly slower than that in normal control cells. (The rate was found to be normal in Fanconi's anemia cells.) The explanation for the retarded chain growth may be either that an enzyme concerned directly with semiconservative DNA replication is defective or that a defective enzyme not itself concerned directly with replication results in disturbed cellular metabolism which in turn affects replication.

Abnormalities, Multiple↗
PubMed1975

Regulation of DNA replication on subchromosomal units of mammalian cells.

The regulation of DNA replication at a subchromosomal level in mammalian cells has been investigated. DNA fiber autoradiographs were prepared from mouse L-929 cells pulse labeled with (3H)thymidine. Initiation events and subsequent chain growth occurring over short stretches (up to three replication units in length) of chromosomal DNA were analyzed. The results show that adjacent units usually initiate replication synchronously and that this synchrony is related to the proximity of initiation sites. In addition, adjacent units are of similar size and the rates of replication fork progression within units and on adjacent units are similar. The rate of fork progression increases with increasing replication unit size. Finally, no evidence for fixed termination sites for the units has been found. These observations suggest that despite large variations in size of replication units, timing of initiation events, and rates of fork progression found in chromosomal DNA as a whole, these processes are closely regulated within subchromosomal clusters of active replication units.

Animals↗
PubMed1975

DNA replication in mammalian cells. Altered patterns of initiation during inhibition of protein synthesis.

The effects of inhibition of protein synthesis by the antibiotics cycloheximide and puromycin on the initiation of DNA replication in mouse L cells were studied. Cellular DNA was pulse labeled with [3H]thymidine of high, then of low specific activity and prepared for fiber autoradiography. Autoradiograms containing multiple (up to four) replication units were analyzed. In control cells, the proportion of replication units that initiated during a 10-min, high specific activity pulse was approximately equal to the proportion initiating immediately before the pulse. The addition of cycloheximide or puromycin at the start of the pulse inhibited the frequency of initiation in that there was a decrease by up to one-third of units initiating during the pulse relative to controls. Replication direction was also altered. Addition of the antibiotics 2 h before the pulse reduced the proportion of bidirectional units observed from 0.98 to 0.70. Antibiotic treatment for 2 h also decreased initiation synchrony in that the proportion of multiunit autoradiograms on which neighboring units showed similar replication patterns (indicating temporally coordinated initiation) was reduced by one-half. These observations indicate that inhibition of protein synthesis alters the normal pattern of DNA initiation.

Cycloheximide↗
PubMed1975

Deoxyribonucleic acid fiber autoradiography as a technique for studying the replication of the mammalian chromosome.

Deoxyribonucleic acid (DNA) fiber autoradiography is a technique that allows analysis of replication events on mammalian chromosomal DNA. 3H-thymidine is used to pulse-label DNA, which is subsequently released from lysed cells and extended linearly over a glass slide. Autoradiograms are produced by exposing the labeled DNA to light-sensitive emulsion. The effects of inhibition of protein synthesis on DNA replication were examined using this technique. Analysis of the autoradiographic patterns has shown that inhibition of protein synthesis with either cycloheximide or puromycin retards the rate of replication fork progression. In addition, these antibiotics after the normal pattern of multifocal initiation on replication units. The spatial interval between active initiation sites is decreased, there is a decay in synchrony of initiation events on subchromosomal clusters of replication units, the decay in synchrony of initiation events on subchromosomal clusters of replication units, the frequency of initiation is inhibited and the frequency of units showing the normal bidirectional mode of replication is decreased. The retarded fork progression and shorter initiation intervals may result either from the continued operation of a subset of replication units resistant to the inhibition of protein synthesis, or be manifestations of the inhibition of protein synthesis on all active sites. The other alterations, decreased synchrony and frequency of initiation and increased unidirectional replication probably occur on all active units when protein synthesis is inhibited.

Autoradiography↗
PubMed1975

Invasive fungal infection in the immunosuppressed host.

Immunosuppression, whether arising as a consequence of disease (haematopoietic and lymphoreticular malignancies) or therapy (against hemograft rejection or malignancy results in a higher than normal incidence of invasive fungal infections such as candidiasis, aspergillosis, mucormycosis and cryptococcosis. Normal host defense mechanisms, both immunologic and non-immunologic, are not fully functional and may contribute to the pathogenesis of these diseases.Candida, normally a superficial colonizer, may invade the gastrointestinal, respiratory or urinary tracts. Aspergillus and mucor species may cause hemorrhagic or necrotising pneumonias and secondarily spread to the brain. Cryptococcus may infect the meninges in the appropriate host. Therapeutics for these diseases is limited. Amphotericin B may alter the course of any of the four diseases. Fluorocystosine has found some use in the treatment of candidiasis and cryptococcosis.

Amphotericin B↗
PubMed1973

DNA replication: direction and rate of chain growth in mammalian cells.

Using pulse labeling techniques with [(3)H]thymidine or [(3)H]cytidine, combined with DNA fiber autoradiography, we have investigated the direction and rate of DNA chain growth in mammalian cells. In general, chain elongation proceeds bidirectionally from the common origin of pairs of adjacent replication sections. This type of replication is noted whether the DNA is labeled first with [(3)H]thymidine of high specific activity, followed by [(3)H]thymidine of low specific activity or the sequence is reversed. Approximately one-fifth of the growing points have unique origins and in these replication units, chain growth proceeds in one direction only. Fluorodeoxyuridine and hydroxyurea both inhibit DNA chain propagation. Fluorodeoxyuridine exerts its effect on chain growth within 15-23 min, while the effect of hydroxyurea is evident within 15 min under conditions where the endogenous thymidine pool has been depleted by prior treatment with fluorodeoxyuridine. Puromycin has no effect on chain growth until 60 min after addition of the compound, even though thymidine incorporation is more than 50% reduced within 15 min. After 2 h of treatment with puromycin, the rate of chain growth is reduced by 50%, whereas thymidine incorporation is reduced by 75%. Cycloheximide reduces the rates of DNA chain growth and thymidine incorporation 50% within 15 min, and, on prolonged treatment, the decrease in rate of chain growth generally parallels the reduction in thymidine incorporation.

Animals↗
PubMed1973

Reovirus: effect of noninfective viral components on cellular deoxyribonucleic acid synthesis.

We determined the effects of noninfective reovirus components on cellular deoxyribonucleic acid (DNA) synthesis. Reovirus inactivated by ultraviolet light inhibited cellular DNA synthesis, whereas reovirus cores and empty capsids did not. Both cores and empty capsids were adsorbed to cells. Adenine-rich ribonucleic acid (RNA) from reovirus, adsorbed to cells in the presence of diethyl-aminoethyl-dextran, produced a partial inhibition of DNA synthesis. RNA was synthesized in the presence of actinomycin D after infection with ultraviolet light-irradiated reovirus, and this RNA synthesis was not due to multiplicity reactivation of virus infectivity. These data suggest that viral structural proteins do not inhibit DNA synthesis and that the inhibition produced by ultraviolet-irradiated virus may be mediated in part or in toto by a newly synthesized viral product.

Animals↗
PubMed1971

Repair replication of HeLa cell deoxyribonucleic acid in cells infected with Newcastle disease virus or mengovirus or treated with puromycin.

We examined repair replication of HeLa cell deoxyribonucleic acid (DNA) in cells infected with mengovirus or Newcastle disease virus or treated with puromycin. Cellular DNA was damaged by ultraviolet light and then pulse-labeled with (3)H-thymidine. Autoradiographic analysis of non-S-phase DNA synthesis (repair replication) showed that there was no inhibition of this process at a time when overall cellular DNA synthesis was severely inhibited by either virus infection or puromycin treatment.

Autoradiography↗