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N R Morris

Publications and source records attributed to N R Morris.

At least 91 records · Page 5Linked to original sources
PubMed1979

Evidence that p-fluorophenylalanine has a direct effect on tubulin in Aspergillus nidulans.

Three temperature-sensitive alleles of benA (benA11, 17 and 21) confer resistance to growth inhibition by p-fluorophenylalanine (FPA). FPA resistance cosegregates with the benA gene. Two back-mutations in benA which cause loss of temperature sensitivity cause loss of FPA resistance, and two indirect suppressors of benA temperature sensitivity also cause FPA resistance to be lost. These results indicate that FPA resistance is an intrinsic property of the benA mutations. The intracellular phenylalanine concentrations of these strains are normal as is their ability to take up phenylalanine from the medium. We conclude that FPA must inhibit growth and cause non-disjunction by a direct effect on the polymerization of tubulin.

Alleles↗
PubMed1977

Assembly of SV40 chromatin in a cell-free system from Xenopus eggs.

A cell-free system is described which assembles chromatin from purified DNA in 1 hr under physiological incubation conditions. It consists of a 145,000 x g (maximum) supernatant fraction from eggs of Xenopus laevis. It converts SV40 DNA to a nucleoprotein which co-sediments with naturally occurring SV40 chromatin and which can be cleaved by micrococcal nuclease to a highly ordered pattern of DNA fragments resembling those from digestion of liver chromatin. It inserts superhelical turns into relaxed, covalently closed DNA. The assembly process is not cooperative. Under limiting conditions, each DNA molecule becomes partially assembled. Assembly does not require replication of the DNA or protein synthesis, but occurs from a stored histone pool of at least 40 ng per egg. Under conditions of DNA excess, assembly becomes dependent upon the amount of exogenous histones added to the incubation. Apart from histones and a nicking-closing activity, chromatin assembly requires an additonal thermolabile factor which is present in the egg supernatant.

Animals↗
PubMed1976

A comparison of the structure of chicken erythrocyte and chicken liver chromatin.

The structure of chicken erythrocyte and chicken liver chromatin has been studied by enzymatic digestion with micrococcal nuclease and DNAase I. Comparison of the fragments produced by brief digestion with micrococcal nuclease indicates that chicken erythrocyte chromatin has a longer nucleosome repeat than chicken liver chromatin, 212 base pairs as opposed to 200 base pairs (bp). More extensive digestion with micrococcal nuclease demonstrates that both tissues have 140 bp mucleosome cores. The difference in the length of the nucleosome repeat must therefore result from a difference in the length of the DNA linker between cores. Chicken erythrocyte chromatin is known to contain a tissue-specific, H1-like histone, H5, and to be genetically dormant. A model is presented to explain how changes in histone H1 could cause changes in the nucleosome repeat length and thereby alter the genetic activity of chromatin.

Animals↗
PubMed1976

Nucleosome structure in Aspergillus nidulans.

The structure of chromatin from Aspergillus nidulans was studied using micrococcal nuclease and DNAase I. Limited digestion with micrococcal nuclease revealed a nucleosomal repeat of 154 base pairs for Aspergillus and 198 base pairs for rat liver. With more extensive digestion, both types of chromatin gave a similar quasi-limit product with a prominent fragment at 140 base pairs. The similarity of the two limit digests suggests that the structure of the 140 base pair nucleosome core is conserved. This implies that the difference in nucleosome repeat lengths between Aspergillus and rat liver is caused by a difference in the length of the DNA between two nucleosome cores. Digestion of Aspergillus chromatin with DNAase I produced a pattern of single-stranded fragments at intervals of 10 bases which was similar to that produced from rat liver chromatin.

Animals↗
PubMed1976

Presence of histones in Aspergillus nidulans.

Five major histone proteins have been extracted from chromatin isolated from purified nuclei of the fungus, Aspergillus nidulans. These proteins had chromatographic properties which were similar to reference calf thymus histones and were purified to electrophoretic homegeneity by gel chromatography of Bio-Gel P10, Bio-Gel P60, and Sephadex G-100. Electrophoresis of these proteins in three different systems (urea-starch, urea-acetic acid polyacrylamide, and discontinuous SDS polyacrylamide) showed that the A. nidulans histones H3 and H4 were nearly identical to calf thymus H3 and H4 with respect to net charge and molecular weight criteria, whereas the fungal histones H1, H2a and H2b were similar but not identical to the corresponding calf thymus histones. Amino acid analysis of A. nidulans histones H2a, H2b, and H4 showed them to be closely related to the homologous calf thymus histones. The mobility patterns of A. nidulans ribosomal basic proteins in three different electrophoretic systems were distinctly different from those of the fungal histones.

Amino Acids↗
PubMed1976

The isolation of nuclei from the filamentous fungus Aspergillus nidulans.

A method has been developed for isolating nuclei from the filamentous fungus Aspergillus nidulans. In this procedure, the mycelia from 14 to 16 h spore-derived cultures of A. nidulans NRI, a stable diploid strain, were frozen with liquid nitrogen and homogenized in a Waring blender. After homogenization, the mycelia were warmed to 4 degrees C and the nuclei were purified from the homogenate by differential centrifugation followed by sedimentation through 2.1 M-sucrose. The final nuclear yield was 15 to 20%, based on DNA estimations. The purified nuclear pellet was free of whole cells. The morphology of the isolated nuclei resembled that of the in situ nuclei; they contained a nucleolus, chromatin, and had a surrounding double membrane. The purified nuclei were characterized by a DNA:RNA:protein ratio of 1:2.8:8.7.

Aspergillus nidulans↗
PubMed1976

Pyrimidine nucleotide metabolism in L5178Y murine leukemia cells: deoxycytidine protection from deoxyguanosine toxicity.

Deoxyguanosine was found to inhibit reduction of uridine phosphate within L5178Y cells. A correlation of this effect with deoxyguanosine-induced inhibition of radioactive incorporation into DNA and inhibition of L5178Y cell growth suggests that depletion of thymidylate pools is involved in the toxicity induced by deoxyguanosine. Deoxycytidine appears to protect from deoxyguanosine toxicity by metabolism to thymidylate via a dCMP deaminase pathway, thus replenishing the thymidylate pools which have been depleted by deoxyguanosine.

Animals↗
PubMed1976

Somatic cell genetic studies of cystic fibrosis.

The expression of the gene coding for the cystic fibrosis ciliary inhibitor has been examined in somatic cell hybrid clonal lines. Hybrids were produced by the fusion of cultured skin fibroblasts from cystic fibrosis patients with mouse RAG and LM (TK-) cell lines. The ciliary inhibitor was detected by the oyster ciliary assay in several primary hybrid clones but not detected in others, indicating the segregation of an associated nuclear gene.

Animals↗
PubMed1975

Pleiotropic effects of a DNA adenine methylation mutation (dam-3) in Escherichia coli K12.

The dam-3 mutation results in a five-fold reduction in the number of 6-methyl-adenine (6-meA) residues in the DNA of E. coli K12 or phage lambda. The DNA of phage fd appears to be devoid of 6-meA when propagated on dam-3 bacteria. The phenotypic differences between dam-3 and dam+ bacteria include: (i) increased free phage in lysogenic dam-3 cultures, (2) increased sensitivity to methyl methanesulfonate (MMS), (3) inviability of dam-3 lex-I strains, (4) lower molecular weight of DNA in dam-3 bacteria in the absence of DNA ligase and (5) increased rate of DNA degradation in dam-3 recA strains.

Adenine↗