Lawrence Bogorad

Proteins of cytoplasmic, chloroplast, and mitochondrial ribosomes of some plants

Abstract The principal objective of this work was to compare the electrophoretic behavior of basic proteins of ribosomes from parts of the same cell. Ribosomes were isolated from maize chloroplasts and cytoplasm as well as from chloroplasts, mitochondria and cytoplasm of mung beans. Using acrylamide gel electrophoresis, basic proteins of these types of ribosomes were compared with those of ribosomes from Escherichia coli and from the blue-green alga Phormidium luridum. In part in agreement with much other work, ribosomes from the cytoplasm of the eukaryotic plants studied were found to be about 80 S and to contain RNAs with molecular weights of about 1.2·10 6 and 0.7·10 6 . The ribosomes of the various chloroplasts and mitochondria, as well as of P. luridum, sediment as approx. 70-S particles and contain RNAs with molecular weights of about 1.1·10 6 and 0.58·10 6 . However, each type of ribosome studied here could be clearly distinguished from any other, including those from E. coli, because of easily observed differences in the electrophoretic behavior of its proteins.

Studies on the biosynthesis of prodigiosin in Serratia marcescens.

Abstract Prodigiosin, the blood-red pigment produced by Serratia marcescens , is a linear tripyrrole. Through a series of isotope incorporation experiments, it has been possible to show that this pigment, although a pryrrolic compound, is not closely related to the porphyrins biosynthetically. It has been demonstrated that δ-aminolevulinic acid a specific precursor of porphyrins, is capable of penetrating the membrane of Serratia marcescens but is not used in the formation of prodigiosin. The possibility that prodigiosin may be derived from four proline units has been studied and found to be untenable. The carboxyl carbon of proline is probably incorporated, as a single carbon unit, into the dipyrrolic precursor of prodigiosin produced by Serratia marcescens mutant 9-3-3. Incorporation experiments utilizing [ 14 C]proline (uniformly labeled), [1- 14 C]proline, and [2- 14 C]proline into both prodigiosin and its dipyrrolic precursor, indicate that C-2, and perhaps the entire ring, of proline is utilized mainly in the formation of the 2-methyl-3-amylpyrrole part of prodigiosin. Hydroxyproline is not utilized in the formation of ring II of prodigiosin. On the basis of [2- 14 C]glycine incorporation into both prodigiosin and its dipyrrolic precursor, it is apparent that the methyl carbon atom of glycine is incorporated with equal efficiency into both halves of the prodigiosin molecule. It is, however, probable that rings I and II are formed by a different mechanism than ring III.

Control Mechanisms in Plastid Development

Publisher Summary This chapter discusses the control mechanisms in plastid development by the nuclear genome through the regulation of the availability of amino acids and of iron. Plastids require some proteins and nucleic acids formed outside the organelle for development, maintenance, and activity. Withholding a particular element or small metabolite such as an amino acid, either experimentally or genetically, results in the formation of abnormal plastids. The location of structural genes for plastid components must be determined from different kinds of data. Similarly, ignorance about nuclear-plastid nutritional interrelationships introduces great difficulties in the determination of the site of control of certain aspects of plastid development. However, the components of the plastid are far from being completely identified, and the molecular genetics of plastids is in a primitive, almost nonexistent, state. The structural and chemical changes that occur during plastid development can be grouped into events discernible in seconds (or less), in minutes, or only after hours of illumination of dark-grown seed plants.This chemical change may be causally related to the first detectable structural effect of illumination, that is, the dissociation of the prolamellar body into a group of loosely packed vesicles. Other structural changes, including vesicle dispersal and the increases in the levels of ribose-phosphate isomerase and ribulose-5-phosphate kinase, also occur only after leaves have been illuminated for hours.