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Biomedical subjects

A Marcus

Publications and source records attributed to A Marcus.

15 recordsLinked to original sources
PubMed1979

RNA synthesis in growing and stationary cells of a culture of Scarlet Rose. Disproportionate synthesis of ribosomal subunits in the stationary state.

RNA synthesis has been investigated in resting and growing cells of a culture of Scarlet rose. The rates of messenger RNA (mRNA) and ribosomal RNA (rRNA) synthesis are five- and ten-fold higher, respectively, in the growing culture. In stationary phase cultures, newly synthesized 26S and 18S rRNA do not appear in the cytoplasm in equimolar amounts. Rather, the 26S/18S ratio of [3H]-uridine labeled rRNA of stationary cells ranged from 0.9 to 1.3 while the ratio of the corresponding fraction from growing cells was 1.6 to 2.0. A similar result was obtained when cells were labeled with [3H-CH3] methionine. Pulse chase experiments demonstrated that the nascent pre-rRNA in resting cells could be chased into polysomes. These data are interpreted to indicate that a major part of the regulation of rRNA synthesis in stationary cells is at the level of the processing of the rRNA transcript.

Cell Cycle↗
PubMed1978

Transformation of monocytes into "fat" cells.

Human peripheral blood leukocytes, when cultured in soft agar give rise to giant (100 to 500 micrometer.) "foam cells." Investigation of the origin and properties of the cells proved that they were derived from monocytes in that the cells adherent to glass after 24 hours in culture were phagocytic, elaborated lysozyme and bore receptors for complement and immunoglobulin. The increment in size was accounted for primarily by large inclusions which on histochemical and biochemical analyses were shown to consist predominantly fo neutral fat. Transformation to fat cells took place in the absence of mitosis. Fc receptors were retained but complement receptors were lost. These observations suggest a role for monocytes in the replacement of hematopoietic tissue by fat in certain hypoplastic states. The cultured monocytes may also serve to facilitate the study of fat synthesis and metabolism in vitro.

Adipose Tissue↗
PubMed1977

A new textbook.

Explore the source record for details and available documents.

Books↗
PubMed1976

Formation of an 80 S methionyl-tRNA initiation complex with soluble factors from wheat germ.

Wheat germ supernatant is resolved into four fractions, C3alpha, C3beta, D and A, all of which are required in addition to elongation EF1 and EF2 for tobacco mosaic virus-RNA (TMV-RNA)-catalyzed amino acid polymerization. Fractions C3beta and D function in the binding of Met-tRNAiMet to the 40 S ribosomal subunit forming an unstable 40 S-Met-tRNA1Met complex that is detected in sucrose gradients only after fixation with glutaraldehyde. Fraction C3beta binds Met-tRNAiMet suggesting that a C3beta-Met-tRNAiMet complex may be an intermediate in the formation of the 40 S complex. GTP is required for the formation of both the C3beta-Met-tRNAiMet and the 40 S-Met-tRNAiMet complexes. In either reaction the nucleotide is partially replaceable by quanyl-5'-yl methylene diphosphonate (GMP-P (CH2) P) while ATP is inactive. When ATP, C3alpha, mRNA, and magnesium acetate (final concentration 3.6 mM) are added to an incubation reaction containing the 40 S-Met-tRNAiMet complex, a stable 80 S-Met-tRNAiMet complex is formed. Radioactive TM virus-RNA binds specifically to the 80 S-Met-tRNAi complex suggesting that mRNA is a component of this complex. C3beta and D, the fractions required in the formation of the 40 S-Met-tRNAiMet complex, are also required for formation of the 80 S-Met-tRNAiMet complex. In addition, unlabeled Met-trnaiMet does not compete significantly with preformed 40 S-Met-tRNAiMet in the 80 S complex-forming reaction. These observations suggest that the 40 S-Met-tRNAiMet complex is an intermediate in the 80 S reaction. The 80 S-Met-tRNAiMet product of the sequential reaction is reactive with puromycin and on this basis it is tentatively considered to be a functional initiation complex. The additional requirement of Fraction A for amino acid polymerization suggests, however, that the initiation process may be more complex.

Binding Sites↗
PubMed1975

Preformed mRNA and the programming of early embryo development.

A significant feature of the early development of fertilized echinoderm and amphibian eggs and germinating seed embryos is the utilization of genetic information that has been previously transcribed during oogenesis and seed ripening. When RNA synthesis is suppressed in the early developing embryos by actinomycin D, cordycepin, or alpha-amanitin, there is no effect on the translation of the "preformed mRNA", only a limited number have been thus far identified; microtubule and histone proteins in the fertilized sea urchin egg and carboxypeptidase and isocritric lyase in germinating cottonseed. Data obtained on the protein synthetic pattern at different times after the onset of development suggest that preformed mRNAs are made available to the translational system in a gradual process, thereby providing a molecular basis for the regulation of development. The possibility is considered that polyadenylation of mRNA, a reaction known to occur early after sea urchin fertilization, is responsible for regulating the release of preformed mRNA. It is shown that this reaction (polyadenylation) can be completely suppressed with little effect on the function of preformed mRNA. Finally, it is suggested, at least for the seed embryo system, that the formation of ATP may be a prerequisite for the activation of protein synthesis.

Amanitins↗
PubMed1975

Textbooks -- a new approach.

A new approach to medical textbooks has been applied by a team comprising a publisher, educationalist, and subject specialist. The binding of the book can be opened so that additional material can be added and the pages rearranged. Illustrations are printed on separate sheets so as to be available for study at any point in the text. An interdisciplinary approach has been adopted throughout and each section of the book examines the subject from a different viewpoint, for example, a disease, a clinical presentation, or an approach to therapy. An important feature is the separation of core material from additional material. Layout and design have been used to facilitate learning and to make possible the use of the book for reference and revision.

Bookbinding↗