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H L Rice

Publications and source records attributed to H L Rice.

8 recordsLinked to original sources
PubMed1990

Positive and negative transcriptional regulatory elements in the early H4 histone gene of the sea urchin, Strongylocentrotus purpuratus.

The early H4 (EH4) histone gene of the sea urchin, Strongylocentrotus purpuratus, is shown to contain at least five positive-responding sequence elements and one negative-responding site which control the level of in vitro transcription in an embryonic nuclear extract. The positive acting elements are: 1) the UHF-1 region, located between -133 and -102 (the site of a strong footprint, due at least in part to the binding of an 85 kD protein factor termed UHF-1); 2) the H4 specific element (H4SE), situated between -62 and -39; 3) a sequence corresponding to a TATA box between -33 and -26 (TAACAATA); 4) the transcriptional initiation site; and 5) an internal sequence element found between +19 and +50. Deletion of, or base changes in, the UHF-1, H4SE, initiation, or internal sequence sites resulted in significant decreases in transcription. Base substitutions in the TATA-like sequence had much less effect, resulting in no more than a 2-fold decrease in transcription, and there was no evidence that alternative initiation sites are utilized in the mutant templates. The negative element (termed the UHF-3 site) is contained within a footprinted region between nucleotides -75 and -56. Base substitutions in this area result in templates that were transcribed at a level 1.2-2.0-fold higher than the wild-type gene. Transcription levels of double UHF-1/H4SE and UHF-1/INR mutants were those expected from additive effects of the individual mutations and there was no suggestion of synergism.

Animals↗
PubMed1989

The effect of external calcium and pH on inositol trisphosphate-mediated calcium release from cerebellum microsomal fractions.

Binding of D-myo-inositol 1,4,5-trisphosphate (InsP3) to rat cerebellum membranes has previously been shown to be stimulated by alkaline pH and inhibited by low concentrations of Ca2+ [Worley, Baraban, Suppatopone, Wilson & Snyder (1987) J. Biol. Chem. 262, 12132-12136]. In the present study, Scatchard analysis of InsP3 binding to cerebellum microsomes indicates that the effects of Ca2+ and pH are exerted through changes in the apparent affinity of the receptor without effects on maximal binding. The influence of extravesicular Ca2+ and pH on InsP3-mediated 45Ca2+ release was investigated. Extravesicular Ca2+ inhibited InsP3-mediated Ca2+ release. The inhibitory effect of Ca2+ was most marked when a sub-optimal concentration of InsP3 was used. An increase in extravesicular pH produced a decrease in the concentration of InsP3 that yielded half-maximal Ca2+ release. Regulation of the affinity of the InsP3 receptor by Ca2+ and pH can qualitatively account for the observed effects of these factors on InsP3-mediated Ca2+ release. Feedback inhibition of InsP3 binding by Ca2+ could provide a mechanism to generate Ca2+ oscillations, particularly under hormonal conditions that produce sub-optimal elevations of InsP3 concentration.

Animals↗
PubMed1989

The relationship between inositol trisphosphate receptor density and calcium release in brain microsomes.

Calcium release in response to D-myo-inositol-1,4,5-trisphosphate (IP3) was compared in two microsomal preparations derived from cerebellum and forebrain, regions of the brain that differ greatly in their density of [3H]IP3 binding sites. The proportion of accumulated calcium released by IP3 was the same in both microsomal preparations when a saturating dose of IP3 was used. However, the concentration of IP3 or a nonhydrolyzable analog required to elicit half-maximal release was lower in cerebellum than in forebrain microsomes. Because cerebellum microsomes contain approximately 15 times the binding density of forebrain microsomes, the data suggest that the Ca2+ release response is proportional to the occupancy of IP3 binding sites. This was also demonstrated by the observation that heparin, an inhibitor of IP3 binding, blocked IP3-mediated Ca2+ release from both cerebellum and forebrain microsomes. The potency of heparin was dependent on IP3 concentration and was independent of receptor density. These data support the view that the receptor present in brain membranes represents the ligand-binding domain of a Ca2+ release mechanism.

Animals↗
PubMed1988

Characteristics of GTP-mediated microsomal Ca2+ release.

Guanosine triphosphate (GTP) can release Ca2+ and enhance responses to D-myo-inositol 1,4,5-trisphosphate (IP3) in crude liver microsomes in the presence of polyethylene glycol (PEG) (Dawson et al. (1986) Biochem. J. 234, 311-315). The mechanism of these responses has been further investigated. GTP gamma S which antagonizes the actions of GTP on microsomes, does not promote Ca2+ re-uptake when added after the completion of GTP-mediated Ca2+ release. However, the effects of GTP could be reversed by washing or dilution of the microsomes. Addition of PEG to the incubation medium promoted the aggregation of microsomes. Electron microscopy provided no evidence for the fusion of microsomal vesicles in the presence or absence of GTP. In the presence of PEG, GTP produced an alteration of the permeability properties of the microsomal membrane as indicated by increased leakage of an intraluminal esterase, a reduction in the mean buoyant density of the vesicles, and a decrease in the latency of mannose 6-phosphate hydrolysis. All three effects developed relatively slowly, whereas the effects of GTP on Ca2+ fluxes occurred more rapidly (complete within 15 min). A low permeability to mannose 6-phosphate was restored upon washing away the GTP. These results suggest that non-specific permeability changes may underly the effects of GTP on Ca2+ release and that, under certain conditions, GTP can reversibly modulate the permeability of a transmembrane 'pore' in microsomal membranes that can pass ions and macromolecules. The possibility that such a pore serves to link IP3-sensitive vesicles with other Ca2+-containing compartments is discussed.

Animals↗
PubMed1976

Friendship Manor: a community geriatrics model.

Models for the delivery of medical services are attracting much attention lately. It appears that geriatrics will become more important in the future. These facts have led to a narrative about the development of a system of medical care for a retirement community in Roanoke, Virginia.

Aged↗