Part I. Protein Synthesis During Chicken Erythrocyte Differentiation. Part II. Studies of Ordered DNA Protein Fibers

Citation

Kabat, David (1967) Part I. Protein Synthesis During Chicken Erythrocyte Differentiation. Part II. Studies of Ordered DNA Protein Fibers. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/EPST-RQ80. https://resolver.caltech.edu/CaltechETD:etd-09202002-093411

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Part I: Protein Synthesis During Chicken Erthrocytes Differentiation. It was the major purpose of this research to study changes of protein synthesis during chicken erythrocyte differentiation. In Chapter 1, erythrocytes from the blood of normal and anemic birds were fractionated by buoyant density centrifugation in bovine serum albumin gradients. It is shown that this procedure fractionates the erythroid cells according to their physiological maturity. Reduction of RNA synthesis, RNA content, and protein synthesis are shown to accompany cell maturation. Inhibition of RNA synthesis with actinomycin D does not affect hemoglobin synthesis in erythroid cells from anemic birds. The two hemoglobins, present within single chicken erythrocytes, appear to be synthesized in constant ratio throughout eiythropoiesis, suggesting that the factors involved (at the genetic and translation levels) in the regulation of these syntheses operate in a cordinate manner. In Chapter 2, it is shown by peptide mapping that the two chicken hemoglobins contain many common amino acid sequences; their genes presumably arose by duplication of common ancestral genes. The site of hemglobin synthesis is the cytoplasmic polyribosome, as shown in part by the similar appearance of autoradiographic peptide maps of [[superscript 14]C] leucine-labeled purified hemoglobin and of [[superscript 14]C] leucine-labeled nascent polypeptides associated with the ribosomes. Labeled growing polypeptide chains, isolated from ribosomes following pulses with [[superscript 3]H] leucine, are shown to be heterogeneous in size, ranging from very small peptides up to complete globin chains. The kinetics of labeling the different sized polypeptides is in agreement with the well-established model of protein synthesis in which amino acids are sequentially polymerized from one end of the growing chains. At 37? in vitro, it requires roughly one minute to synthesize a complete globin chain (approximately 150 amino acids). It is also demonstrated that both histone and non-histone chromosomal proteins are synthesized in non-dividing avian erythrocytes. The histones synthesized are, selectively, the "arginine-rich" histones. In Chapter 3, a study is made of the nuclear hemoglobin of chicken erythrocytes. One percent of the total cell hemoglobin remains associated with nuclei isolated in low ionic strength solutions, but this bound hemoglobin fraction can be extracted with 0.14 hi NaCl. A ubiquitous and widely-studied class of nuclear protein molecules from plant and animal cells ("nuclear soluble proteins") has similar nuclei-binding properties. It is demonstrated that the bound hemoglobin molecules consist exclusively of one of the two hemoglobin types, that they are complexed to the erythrocyte chromosomes, and that they co-sediment with the chromatin in sucrose gradients. Part II: Studies of Ordered DNA Protein Fibers. Mixtures of-chicken hemoglobin and DNA or horse heart cytochrome c and DNA form highly-ordered and tightly-packed fibrous complexes only in the presence of divalent metal ions. Polarization and electron microscopy are used to demonstrate that the DNA molecules are strongly oriented parallel to the fiber axes. Polarized visible absorption spectra are used to determine the hemoprotein orientation in the fibers; spectra of several derivatives of horse hemoglobin crystals and also horse heart ferricytochrome c crystals are analyzed as controls. A model for the role of divalent metal ions in the tightly-packed nucleoprotein fibers is deduced from these experiments. The well-known strong stabilizing effects of divalent metal ions on tightly-packed ribosome and chromosome structures are also discussed.

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