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Biomedical subjects

A E Mirsky

Publications and source records attributed to A E Mirsky.

At least 19 recordsLinked to original sources
PubMed1973

Accessibility of DNA in chromatin to DNA polymerase and RNA polymerase.

The accessibility of DNA in chromatin to both exogenous DNA polymerase and RNA polymerase is slight when compared to isolated DNA. DNA in extracted chromatin is somewhat more accessible to these enzymes than is DNA in the chromatin of isolated nuclei; and the DNA template of chromatin is more accessible to DNA polymerase than to RNA polymerase. In these experiments we have given much attention to the technique of scintillation counting, since artifacts arising in this procedure can lead to erroneous conclusions.

Adenosine Triphosphate↗
PubMed1973

Effects of selective extraction of histones on template activities of chromatin by use of exogenous DNA and RNA polymerases.

Exogenous DNA and RNA polymerases were used to measure the template activity of DNA in chromatin in isolated thymus nuclei from which lysinerich or arginine-rich histones were selectively extracted. Measurements were on nuclei containing 20-1200 mug of DNA per ml, the distinctions becoming clear at the higher concentrations. Experiments with RNA polymerase showed only moderate increases in template activity upon extraction of histone, although the removal of lysinerich histone had a greater effect than that of arginine-rich histone. DNA polymerase action on nuclei minus lysinerich histone achieved high results, exceeding even those on DNA itself.

Animals↗
PubMed1973

Addition of histones to histone-depleted nuclei: effect on template activity toward DNA and RNA polymerases.

The ability of histones to block the accessibility of DNA in chromatin to DNA and RNA polymerases was measured by addition of lysine-rich or arginine-rich histones to nuclei selectively depleted of these histones. By this procedure nuclei were obtained in which all of the original lysine-rich histone in the chromatin was replaced by arginine-rich histone. Conversely in other nuclei, additional lysine-rich histone replaced some of the endogenous arginine-rich histone. Lysine-rich histone was much more effective than arginine-rich histone in blocking accessibility to DNA polymerase. Both classes of histone inhibited template activity toward RNA polymerase to a similar extent. In addition to lysine-rich histone and total arginine-rich histone, phosphorylated lysine-rich histone, two fragments of lysine-rich histone produced by cleavage with N-bromosuccinamide, and fractions IIB and IV of arginine-rich histone were added to histone-depleted nuclei. With both DNA and RNA polymerases as probes, no differences in inhibition of template activity were found when native lysine-rich histone was compared to phosphorylated lysine-rich histone. Similarly, fractions IIB and IV were indistinguishable from total arginine-rich histone. On a molar basis, the carboxyl fragment of lysine-rich histone was as effective as intact lysine-rich histone only when the amino fragment was added to it. By itself, the amino portion of lysine-rich histone was without inhibitory effect in the RNA polymerase assay and resulted in only slight inhibition of template activity toward DNA polymerase.

Arginine↗
PubMed1972

Blocking by histones of accessibility to DNA in chromatin: addition of histones.

The blocking effect of histones on accessibility of DNA to DNase has been studied by addition of various histones to chromatin in intact or histone-depleted thymus nuclei (those from which all lysine-rich histone was removed and those from which much of the arginine-rich histone was removed) and to deoxyribonucleoprotein (chromatin) extracted from nuclei. In each case lysine-rich histone, weight for weight, blocks accessibility more effectively than does arginine-rich histone. Fractions of the arginine-rich histone differ considerably from each other in their blocking efficacy. Phosphorylation of lysine-rich histone tempers its blocking effectiveness.

Animals↗
PubMed1972

Blocking by histones of accessibility to DNA in chromatin.

The effect of histones on accessibility of DNA to DNase in chromatin of thymus nuclei has been studied by selective extraction of either lysine-rich or arginine-rich histones. It was found that all histones block accessibility but that, weight for weight, lysine-rich histones block much more effectively than do arginine-rich histones. We point to the contrast between accessibility of DNA to DNase and of DNA to RNA polymerase, and to what may be the similarity between accessibility to DNase and DNA polymerase.

Animals↗
PubMed1971

The structure of chromatin.

The DNA in chromatin of isolated thymus nuclei, and in two different preparations of deoxyribonucleoprotein extracted from chromatin, has been digested with DNase. By variation of the time of reaction and the concentration of enzyme, and by comparison of the action of the enzyme on (protein-free) DNA with its action on DNA complexed with protein in chromatin and deoxyribonucleoprotein, it was found that most, if not all, of the DNA is linked to protein. The linkage is loose, as shown by the fact that all the DNA is accessible to the enzyme; however, the wide variations in accessibility in a given complex show that the looseness of the DNA-protein link varies considerably. Accessibility of DNA in one type of deoxyribonucleoprotein preparation is greater than it is in chromatin, while in the other type it is less than in chromatin.

Animals↗
PubMed1969

Regulation of liver tyrosine aminotransferase by endogenous factors in the mouse.

The levels of mouse liver tyrosine aminotransferase (TAT) are shown to increase rapidly and transiently during and after various challenges (e.g., exposure to cold or shaking) to the homeostatic machinery of the fasted mouse. The increase of TAT is dependent on gene activity. Recent feeding and adrenalectomy are shown to inhibit the induction of TAT during the challenge of cold.

Adrenal Glands↗
PubMed1969

Ageing and the regulation of cell activities during exposure to cold.

The inability to maintain body temperature and a selective pattern of changes in the regulation of cell activities were revealed by briefly exposing ageing C57B1/6J male mice to cold (10 degrees C). The induction of liver tyrosine aminotransferase (TAT) during exposure to cold (a gene-dependent process) was markedly delayed in senescent mice (26 months old) as compared with younger mice (3-16 months old); after the delay, the rate of increase of TAT was similar to that prevailing in younger mice. Direct challenge of the liver with injections of corticosterone or insulin elicited the induction of TAT on an identical time course in young and senescent mice. These experiments provide an example of an age change in a gene-dependent cell process (the delayed induction of TAT in senescent mice during exposure to cold) which is not due to a change in the potential of the genome for responding when exogenous stimulae are supplied (injection of hormones). In contrast to the age-related change in liver cell activities, no significant changes were found in the secretion of corticosterone during exposure to cold. Although the seat of these selective age-related changes in the regulation of cell activities remains unclear, it is argued that generalized damage to the genome of cells throughout the body is not involved. The results of this and other studies showing the selective effect of age on cell activities are considered in terms of the concept that many cellular age changes represent the response of cells to primary age-related changes in humoral factors in the internal environment of the body.

Adrenal Glands↗
PubMed1968

Histone acetylation in insect chromosomes.

Acetylation of histones takes place along the salivary gland chromosomes of Chironomus thummi when RNA synthesis is active. It can be observed but not measured quantitatively by autoradiography of chromosome squashes. The "fixatives" commonly used in preparing squashes of insect chromosomes preferentially extract the highly acetylated "arginine-rich" histone fractions; the use of such fixatives may explain the reported absence of histone acetylation in Drosophila melanogaster.

Acetates↗