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Biomedical subjects

A Marcus

Publications and source records attributed to A Marcus.

At least 91 records · Page 5Linked to original sources
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

Cytokinin effects on growth of quiescent tobacco pith cells.

Excised pith tissue from Nicotiana glauca or the tumor-prone hybrid N. glauca x N. langsdorffii has no growth requirement for exogenous cytokinins. Addition of kinetin to cultures of these lines results in growth inhibition at a kinetin concentration 1000-fold lower than the optimal level for kinetin-requiring lines. Cytological comparison of the kinetin-inhibited 2N hybrid and glauca tissues with pith from the kinetin-requiring N. tabacum var. Wisconsin 38 suggests that the nature of the cytokinin action is similar in both situations and that the primary function of cytokinin, when it stimulates growth, may be to curtail cell expansion, thereby facilitating a balance of cell expansion and division requisite for maximal growth.

Journal Article↗
PubMed1975

Transcription of Ribosomal and Messenger RNAs in Early Wheat Embryo Germination.

Germinating wheat embryos (Triticum aestivum L). synthesize both ribosomal and messenger RNA at the earliest times after the onset of germination. The rates of synthesis of these two RNAs are determined at various stages in germination by an analysis of newly synthesized radioactive RNA on oligo(dT)-cellulose. The rate of messenger RNA synthesis is essentially constant throughout 18 hours of germination, while that of ribosomal RNA synthesis increases steadily, particularly after the onset of cell expansion (6 hours), reaching at 16 to 18 hours, a rate of synthesis between 5- and 20-fold greater than that observed at the earliest stages. The net effect is a relative decrease in the fraction of transcribed high molecular weight RNA that is mRNA. Throughout the first 7 hours of germination, mRNA is 25 to 30% of the transcribed fraction, whereas by 16 to 18 hours it has declined to a level of 4 to 8%.

Journal Article↗
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↗
PubMed1974

Activation of Protein Synthesis upon Dilution of an Arachis Cell Culture from the Stationary Phase.

When a stationary phase cell culture of Arachis hypogaea L. is diluted into fresh media, there occurs a 10-fold increase in the rate of protein synthesis. The kinetics of the activation of amino acid-incorporating capacity show a lag of 10 to 15 minutes with maximal activity reached at 2 hours after dilution. The activation of protein synthesis is oxygen-dependent and is accompanied by a 2- to 4-fold increase in polyribosome content, as well as by a 3- to 4-fold increase in the rate of mRNA synthesis. Ribosomal function, as ascertained by determination of ribosomal transit time, is about 2.5 times more efficient in 2-hour diluted cultures as in cells immediately after dilution. These observations indicate that a very early response in the transition of plant cell cultures from the stationary state is an increased capacity for protein synthesis. At a molecular level, this increase in protein synthetic capacity is due in part to an increased mobilization of mRNA into polyribosomes and in part to a more efficient ribosomal translational capacity.

Journal Article↗
PubMed1974

Rapid Increase in Adenosine 5'-Triphosphate during Early Wheat Embryo Germination.

The ATP content of isolated wheat (Triticum aestivum L. var. Polk) embryos increases 5-fold during the first 30 minutes and 10-fold during the first hour of germination to 80% of maximum. The ATP level remains at approximately 800 nanomoles per gram of tissue during the next 15 hours. ADP, AMP, and total adenosine phosphates decrease between 1 and 6.5 hours, while adenylate energy charge increases from 0.6 to 0.8 and remains constant. The rapid increase in ATP during imbibition is consistent with the energy requirement for polyribosome formation and protein synthesis during the first hours of germination. A method for determining nanomole quantities of ATP in tissue extracts by isotopic dilution of gamma-(32)P-ATP in the hexokinase reaction is outlined.

Journal Article↗