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Biomedical subjects

H F Epstein

Publications and source records attributed to H F Epstein.

At least 73 records · Page 4Linked to original sources
PubMed1978

The moderately repetitive DNA sequences of Caenorhabditis elegans do not show short-period interspersion.

In these studies we show that the moderately repetitive DNA sequences of Caenorhabditis elegans are not arranged in the characteristic short-period interspersion pattern of most eukaryotes. Rather, the moderately repetitive sequences are arranged in long arrays as in Drosophila and Apis. These findings indicate that this type of arrangement is more phylogenetically diverse and hence less exceptional than previously believed.

Animals↗
PubMed1978

Muscle development in Caenorhabditis elegans: mutants exhibiting retarded sarcomere construction.

We have studied the structural changes within the body-wall muscle cells of Caenorhabditis elegans during postmitotic development. In wildtype, the number of sarcomeres progressively increases, and each sarcomere appears to grow in length and depth continuously during this period. In mature wild-type cells, the anterior-most body-wall muscle cells have 6--7 sarcomeres; the rest have 9--10 sarcomeres per cell. Twelve mutants in the unc-52 II gene exhibit markedly retarded sarcomere construction and progressive paralysis. Several unc-52 mutants, such as the severely paralyzed SU200, produced only 2--3 sarcomeres per body-wall muscle cell, while the other mildly paralyzed unc-52 mutants, such as SU250, build 3--4 sarcomeres per muscle cell. Other structures such as the pharynx and even the noncontractile organelles of the body-wall muscle cells do not appear to be structurally or functionally altered. The unc-52 body-wall sarcomeres become moderately disorganized as they are outstripped by cell growth; sufficient order is preserved, however, so that the majority of thick and thin filaments still interdigitate. The myosin heavy chains of SU200 body-wall muscle fail to accumulate normally, while the pharyngeal myosin heavy chains do not appear to be specifically affected. This biochemical result correlates well with the specificity of morphological changes in the mutant. A model is discussed in which the biochemical and morphological deficits are explained by a simple regulatory mechanism.

Animals↗
PubMed1977

Actin from the nematode, Caenorhabditis elegans, is a single electrofocusing species.

We have prepared actin from wild type Caenorhabditis elegans animals by three procedures: a purification dependent on the ability of actin to form F-actin, affinity chromatography which preferentially binds G-actin, and co-precipitation of an actin-myosin complex by antimyosin antibodies. Each preparation yields a single electrofucsing species of actin. Comparison of actin from C. elegans embryos and animals reveals that embryos also have the same single electrofocusing species of actin.

Actins↗
PubMed1977

Actin and myosin-linked calcium regulation in the nematode Caenorhabditis elegans. Biochemical and structural properties of native filaments and purified proteins.

Calcium regulation of actomyosin activity in the nematode, Caenorhabditis elegans, has been studied with purified proteins and crude thin filaments. Actin and tropomyosin have been purified from C. elegans and shown to be similar in most respects to actin and tropomyosin from rabbit skeletal muscle. The actin comigrates with rabbit actin on polyacrylamide-sodium dodecyl sulfate gel electrophoresis, forms similar filaments and paracrystals, and activates the Mg2+-ATPase of rabbit myosin heads as efficiently as rabbit actin. Nematode tropomyosin has a greater apparent molecular weight (estimated by mobility on polyacrylamide-sodium dodecyl sulfate gels) than the rabbit protein, yet it forms Mg2+-paracrystals with a slightly shorter periodicity. Native thin filaments extracted from nematodes activate rabbit myosin subfragment 1 Mg2+-ATPase in a calcium sensitive manner; the extent of activation is threefold greater in 0.2 mM CaCl2 than in the absence of calcium. This observation suggests that the thin filaments contain components which are functionally equivalent to vertebrate troponins. Calcium is also required for maximal activation of the Mg2+-ATPase of purified nematode myosin by pure rabbit F-actin. C. elegans therefore has both myosin and thin filament-linked calcium regulatory systems. The origin of the actin, tropomyosin, and myosin from different tissues and the use of genetic analysis to answer questions about assembly and function in vivo are discussed.

Actins↗
PubMed1977

Myosin and paramyosin of Caenorhabditis elegans: biochemical and structural properties of wild-type and mutant proteins.

Myosin and paramyosin have been purified from the nematode, Caenorhabditis elegans. The properties of the myosin in general resemble those of other myosins. The native molecule is a dimer of heavy (210,000 dalton) polypeptide chains and contains 18,000 and 16,000 dalton light chains. When rapidly precipitated from solution, it forms small, bipolar aggregates, about 150 nm long, consistent with the expected molecular structure of a rigid rod with a globular head region at one end. Its ATPase activity is stimulated by Ca2+ and EDTA. The myosin binds to F actin in a polar and ATP-sensitive manner, and the Mg2+-ATPase is activated by either F actin or nematode thin filaments. Dialysis of myosin to low ionic strength produces very long filaments. When a myosin-paramyosin mixture is dialyzed under the same condtions, co-filaments form which consist of a myosin cortex, surrounding a paramyosin core. Some properties of myosin from the mutants E675 and E190, which have functionally and structurally altered body wall muscles, are compared with those of wild-type myosin. These myosins of these results are discussed in terms of the myosin heavy chain composition.

Actins↗
PubMed1976

Myosin-paramyosin cofilaments: enzymatic interactions with F-actin.

The interaction between paramyosin and myosin has been studied by enzymological methods. Clam adductor paramyosin inhibits the actin-activated, Mg2+-requiring ATPase of both clam adductor and rabbit skeletal muscle myosins. Myosin and paramyosin must be rapidly coprecipitated for this inhibition. Incubation with F-actin in the absence of ATP does not alter this effect. This inhibition follows a hyperbolic function with respect to paramyosin concentration. Slow precipitation by dialysis of myosin and paramyosin together leads to copolymers with actin-activated ATPase equivalent to that of slowly formed myosin filaments. Both kinds of slowly formed filaments have enzymatic properties distinct from those of the rapidly precipitated proteins. Paramyosin is competitive with F-actin for their effects upon myosin. The apparent affinity of myosin for F-actin is markedly reduced by association with paramyosin, but the extrapolated maximal velocity of actomyosin is unaffected. The specificity of this inhibition is strongly suggested by marked quantitative differences between native and cleaved paramyosins. No inhibition of intrinsic myosin ATPase by paramyosin is seen. These studies suggest that at least two types of condition-dependent association between myosin and paramyosin are possible. One class of interactions is associated with enzymic inhibition in rapidly coprecipitated filaments, whereas slowly formed cofilaments exhibit catalytic activity similar to that of identically treat-d myosin and have a characteristic 14.5 nm axial repeat.

Actins↗
PubMed1975

Interaction of myosin and paramyosin.

The interaction of myosin and paramyosin was investigated by enzymological and ultrastructural techniques. The actin-activated Mg+2 ATPase of rabbit skeletal muscle myosin can be inhibited by clam adductor paramyosin. Both proteins must be rapidly coprecipitated to form filaments for this inhibition. Slowly formed cofilaments are fully activatable by F-actin. In both cases, the cofilaments possess unique structural characteristics when compared to homofilaments. The mode of inhibition appears to be competitive when different concentrations of paramyosin and F-actin are compared. The apparent affinity of the myosin heads for actin is reduced by the presence of paramyosin within rapidly reconstituted thick filaments. These results suggest that paramyosin may serve as part of a relaxing mechanism within invertebrate muscles. It is unlikely that paramyosin plays a role in the initiation and maintenance of catch within specialized molluscan muscles.

Actins↗
PubMed1971

Folding of staphylococcal nuclease: magnetic resonance and fluorescence studies of individual residues.

The reversible unfolding and folding of staphylococcal nuclease in the acid transition has been studied by 220 MHz proton magnetic resonance spectroscopy. The values of area, line-width, and chemical shift of each of the imidazole C2 proton resonances of the four histidine residues have been measured in this transition. The change of areas of three histidine resonances and the change of fluorescence of the single tryptophan residue, as a function of pH, appear to follow a single equilibrium. In contrast, a fourth histidine resonance follows a biphasic transition. These findings indicate that local conformational changes can be detected by magnetic resonance spectroscopy in the cooperative transition of the overall structure.

Amino Acid Sequence↗