The Dictyostelium ribosome: biochemistry, molecular biology, and developmental regulation.

This is the first comprehensive review of ribosomes in the cellular slime mold Dictyostelium discoideum. The physicochemical, biochemical, cellular, molecular, and developmental properties are reviewed. Several features demonstrate that a unique class of ribosomes exists in this organism, and a study of these ribosomes will be important to decipher special features of translational regulation, and evolution of the organelle in the eukaryotic kingdom.     

Phenolic acids in groundnut seed exudates

Summary Seed exudates were collected aseptically and extracted for phenolic acids. Paper chromatographic analysis revealed the presence of eleven phenolic compounds.Department of Botany, S.V. University, Tirupati-517502, Andhra Pradesh, India.     

Acidic ribosomal proteins of Dictyostelium discoideum that show electrophoretic similarity to Escherichia coli proteins L7 and L12

This study documents the presence of three acidic proteins, A1 (pI 4.95), A2 (pI 4.85), and A3 (pI 4.70), in Dictyostelium discoideum ribosomes. All three proteins showed an apparent molecular mass of 13,000 by two-dimensional, sodium dodecyl sulfate gel electrophoresis. They were selectively released by treatment of ribosomes with 50% ethanol -1 M NH4Cl. The amino acid composition of A1, A2, and A3 were identical and indicated a predominant amount of alanine. All the above properties are shared by Escherichia coli proteins L7 and L12 and acidic ribosomal proteins in many eukaryotes. Unlike other eukaryotic systems, the acidic proteins of D. discoideum were found associated with the 40S rather than the 60S ribosomal subunit. Acidic proteins analogous in size and electrophoretic mobility to those of D. discoideum were also detected in several other cellular slime mold strains. Not one of the cellular slime mold acidic proteins reacted with antibodies to E. coli proteins L7 and L12 in immunodiffusion tests. In D. discoideum, the distribution of acidic proteins was altered during development. Amoebae contained all three proteins. In spores, A1 was absent and the relative amounts of A2 and A3 were lower than in amoebae. In addition, nine other acidic ribosomal proteins exhibited differences between vegetative amoebae and spores.     

Extracellular calcium-dependent and -independent effects of adenosine in bovine coronary artery

Adenosine relaxes the coronary arteries of various species through A2 receptors. The aim of the present investigation was to evaluate the relaxing effects of adenosine in relation to the role of calcium in bovine coronary arteries by studying the vasodilatory effect of adenosine in normal and calcium-free medium and on calcium-45 efflux into calcium-free medium. Acetylcholine (ACh) and norepinephrine (NE) were used to induce tone in coronary artery rings. Adenosine, 5'-(N-ethylcarboxamido)adenosine (NECA), and N6-(L-phenylisopropyl)adenosine (L-PIA) produced concentration-dependent relaxations of the coronary artery rings. Both in normal and calcium-free medium, the order of potency for adenosine analogs (NECA greater than L-PIA greater than adenosine) was similar and 8-phenyltheophylline antagonized the relaxation responses to adenosine and its analogs. Removal of extracellular calcium shifted the concentration-response curves to the right in a parallel fashion, slowed the rate of relaxation, and in NE contracted rings reduced the maximum responses for adenosine and its analogs. In calcium-free medium, adenosine was without an effect on calcium-45 efflux in the presence of ACh. However, adenosine inhibited the stimulated calcium-45 efflux induced by NE. The data suggest that the vasodilatory action of adenosine in bovine coronary smooth muscle has both extracellular calcium-dependent and -independent components.     

Altered specificity of synthesis of guanosine tetraphosphate (ppGpp) and pentaphosphate (ppGpp) by salt-washed ribosomes

Salt-washed ribosomes from $\text{Escherichia coli}$, plus stringent protein, form more ppGpp than pppGpp from GTP at all times, but unwashed ribosomes are shown to synthesize primarily pppGpp as the initial product.     

Unintegrated viral sequences in rat cells transformed by simian virus 40 and a temperature sensitive A gene mutant

The status of viral sequences in rat cells transformed by simian virus 40 (SV40) and its temperature sensitive A gene mutant was investigated. Agarose gel electrophoresis of cell DNA prepared from clones picked from soft-agar and blot hybridization showed that sequences specific to SV40 genome were present both as integrated and unintegrated structures in rat clones. Digestion of rat cell DNA with various endonucleases with or without recognition sites in SV40 DNA and analysis indicated that the unintegrated viral genomes existed as full-length, covalently closed circular molecules. No differences in the free viral genomes were apparent between the clones transformed by the wild type and the mutant virus. The importance of the existence of free viral genomes in nonpermissive cells is discussed.