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S Dalton

Publications and source records attributed to S Dalton.

46 records · Page 3Linked to original sources
PubMed1986

Chicken histone genes retain nuclear matrix association throughout the cell cycle.

The association between histone genes and the nuclear matrix (NM) during periods of high (S-phase) and low (non-S-phase) transcriptional activity has been investigated with synchronized cells from a chicken erythroid cell line (abbreviated ts34). By DNase I and restriction enzyme analysis, these studies reveal that both core and linker histone genes (represented by H2A and H1 genes respectively) are attached to the NM independent of their transcriptional activity during the cell-cycle. The tissue-specific histone gene H5, expressed constitutively, is nuclear matrix (NM)-associated in ts34 cells but is found in the supernatant (S/N) fractions of a non-erythroid T-cell line. Furthermore, we show that DNA sequences necessary for NM-attachment of the H5 gene lie within a 780 base pair region spanning part of the coding and 5' non-translated region. Of the three non-histone genes investigated, beta-actin sequences are expressed and are NM-attached, feather keratin genes are not expressed and predominate in the S/N, and beta-globin genes although not expressed in the ts34 cell line used were found in the NM fraction. In this case the association may be fortuitous or may reflect an early event prior to transcription of globin genes in differentiating erythroid cells. These results generally support the notion that actively transcribed genes are NM-attached, but that attachment per se is not synonymous with transcription.

Actins↗
PubMed1986

Transcription of the histone H5 gene is not S-phase regulated.

Levels of the tissue-specific linker histone H5 are elevated in mature erythroid cells as compared with levels in dividing cells of the same lineage. We examined levels of H5 mRNA in relation to the cell cycle in early erythroid cells transformed by avian erythroblastosis virus to determine whether the gene for this unusual histone is S-phase regulated. Northern blotting analyses revealed that during the cell cycle steady-state levels of H5 mRNA remained relatively constant in contrast to levels of the major core and H1 mRNAs which increased approximately 15-fold during S phase. In vitro pulse-labeling experiments involving nuclei isolated from synchronized cells at various stages of the cell cycle revealed that transcription of the H5 gene was not initiated at any particular stage of the cell cycle but was constitutive. In contrast, transcription of the H2A gene(s) initiated in early S phase, was present throughout the DNA replicative phase, and was essentially absent in G1 and G2 phases.

Alpharetrovirus↗
PubMed1985

Heroin abuse.

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Community Health Nursing↗
PubMed1984

Effects of lysophospholipids on Ca2+ transport in rat liver mitochondria incubated at physiological Ca2+ concentrations in the presence of Mg2+, phosphate and ATP at 37 degrees C.

Lysophospholipids caused the release of 45Ca2+ from isolated rat liver mitochondria incubated at 37 degrees C in the presence of low concentrations of free Ca2+, ATP, Mg2+, and phosphate ions. The concentrations of lysophosphatidylethanolamine, lysophosphatidylcholine, lysophosphatidic acid and lysophosphatidylinositol which gave half-maximal effects were 5, 26, 40 and 56 microM, respectively. The effects of lysophosphatidylethanolamine were not associated with a significant impairment of the integrity of the mitochondria as monitored by measurement of membrane potential and the rate of respiration. Lysophosphatidylethanolamine did not induce the release of Ca2+ from a microsomal fraction, or enhance Ca2+ inflow across the plasma membrane of intact cells, but did release Ca2+ from an homogenate prepared from isolated hepatocytes and incubated under the same conditions as isolated mitochondria. The proportion of mitochondrial 45Ca2+ released by lysophosphatidylethanolamine was not markedly affected by altering the total amount of Ca2+ in the mitochondria, the concentration of extramitochondrial Mg2+, by the addition of Ruthenium Red, or when oleoyl lysophosphatidylethanolamine was employed instead of the palmitoyl derivative. The effects of 5 microM-lysophosphatidylethanolamine were reversed by washing the mitochondria. The possibility that lysophosphatidylethanolamine acts to release Ca2+ from mitochondria in intact hepatocytes following the binding of Ca2+-dependent hormones to the plasma membrane is briefly discussed.

Adenosine Triphosphate↗
PubMedDate not supplied

Forkhead transcription factors, Fkh1p and Fkh2p, collaborate with Mcm1p to control transcription required for M-phase.

BACKGROUND: The 'CLB2 cluster' in Saccharomyces cerevisiae consists of approximately 33 genes whose transcription peaks in late G2/early M phase of the cell cycle. Many of these genes are required for execution of the mitotic program and then for cytokinesis. The transcription factor SFF (SWI5 factor) is thought to regulate a program of mitotic transcription in conjunction with the general transcription factor Mcm1p. The identity of SFF has yet to be determined; hence further understanding of the mechanisms that regulate entry to M phase at the transcriptional level requires characterization of SFF at the molecular level. RESULTS: We have purified the biochemical activity corresponding to SFF and identified it as the forkhead transcription factor Fkh2p. Fkh2p assembles into ternary complexes with Mcm1p on both the SWI5 and CLB2 cell-cycle-regulated upstream activating sequence (UAS) elements in vitro, and in an Mcm1 p-dependent manner in vivo. Another closely related forkhead protein, Fkh1p, is also recruited to the CLB2 promoter in vivo. We show that both FKH1 and FKH2 play essential roles in the activation of the CLB2 cluster genes during G2-M and in establishing their transcriptional periodicity. Hence, Fkh1p and Fkhp2 show the properties expected of SFF, both in vitro and in vivo. CONCLUSIONS: Forkhead transcription factors have redundant roles in the control of CLB2 cluster genes during the G2-M period of the cell cycle, in collaboration with Mcm1p.

Cell Cycle Proteins↗