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M D Sargent

Publications and source records attributed to M D Sargent.

26 records · Page 2Linked to original sources
PubMed1976

Circular dichroism of intermediate subviral particles of reovirus. Elucidation of the mechanism underlying the specific monovalent cation effects on uncoating.

1. Circular dichroic (CD) spectra of purified intermediate subviral particles of reovirus were determined in the presence of different monovalent cations. 2. The CD spectra reveal that reo intermediate subviral particles can exist in two conformationally different forms. The two forms are readily distinguished by comparison of their ellipticities in the wavelength regions 210 nm and 220 nm, with a Na+-induced form exhibiting a reduced negative ellipticity relative to a Cs+-induced form. 3. The transition between the Na+- and Cs+-induced forms is reversible by manipulation of the species of monovalent cation present and appears to be temperature independent. 4. Temperature variation studies on dilute suspensions of particles indicate that the Na+-induced form is stable, whereas the Cs+-induced from undergoes a second transition, temperature dependent and irreversible, to become a viral core. 5. A model is presented relating these observations to the known properties of reovirus uncoating and transcriptase activation.

Cesium↗
PubMed1973

Extraordinary effects of specific monovalent cations on activation of reovirus transcriptase by chymotrypsin in vitro.

Activation of reovirus transcriptase activity, latent in intact virions, by digestion of purified virions with chymotrypsin (CHT) in vitro shows a stringent requirement for specific monovalent cations. Cs(+), Rb(+), or K(+) ions are capable of facilitating activation by chymotryptic digestion. Na(+), Li(+), or NH(4) (+) ions are not capable of facilitating the CHT activation of polymerase activity and are antagonistic towards the effects of the facilitating ions. The data indicate that the effect of the cations is exerted on activation of the polymerase activity by CHT as opposed to an effect on polymerization per se. This effect may be important biologically in that it provides a mechanism whereby the virion can sense whether it is in an intracellular or an extracellular environment and thereby can avoid premature uncoating.

Ammonia↗
PubMed1973

New intermediate subviral particles in the in vitro uncoating of reovirus virions by chymotrypsin.

Reovirus virions, grown in suspension cultures of L cells and extensively purified by density gradient and velocity gradient centrifugation after their release from cell debris by fluorocarbon extraction, are characterized by a mean particle diameter of 73 nm and a density in CsCl of 1.36 to 1.37 g/cm(3). Treatment of intact virions by chymotrypsin (CHT) digestion in vitro converts them to subviral particles (SVP) having characteristics which are determined by the species of monovalent cation present during the digestion. In the presence of Cs(+) ions, CHT converts the virions to SVP of mean diameter 51 nm and density 1.43 to 1.44 g/cm(3). In the presence of K(+) ions, the conversion is to SVP of diameter 51 nm and density 1.39 to 1.40 g/cm(3). The SVP made in the presence of either Cs(+) or K(+) possess an extremely active RNA polymerase and nucleoside triphosphate phosphohydrolase (NTPase) activity in vitro and are resistant to further digestion by CHT. Treatment of intact virions with CHT in the presence of Na(+) or Li(+) ions results in their conversion to SVP of mean diameter 64 nm and density 1.37 to 1.38 g/cm(3). Such SVP are not active in in vitro RNA synthesis or NTP hydrolysis and are resistant to further digestion by CHT even during prolonged exposure to high concentrations of enzyme. Addition of Cs(+) or K(+) ions to the digestion mixture allows conversion of the 64-nm diameter SVP to 51-nm diameter SVP in which the RNA polymerase and NTPase are active in vitro. Analysis of the proteins present in intact virions and in the different SVP reveals clear differences which indicate that the conversions are accomplished by removal or cleavage of particular species of polypeptides.

Animals↗