Isolation, DNA sequence, and regulation of a Saccharomyces cerevisiae gene that encodes DNA strand transfer protein alpha.

DNA strand transfer protein alpha (STP alpha) from meiotic Saccharomyces cerevisiae cells promotes homologous pairing of DNA without any nucleotide cofactor in the presence of yeast single-stranded DNA binding protein. This gene (DNA strand transferase 1, DST1) encodes a 309-amino-acid protein with a predicted molecular mass of 34,800 Da. The STP alpha protein level is constant in both mitotic and meiotic cells, but during meiosis the polypeptide is activated by an unknown mechanism, resulting in a large increase in its specific activity. A dst1::URA3/dst1::URA3 mutant grows normally in mitotic media; however, meiotic cells exhibit a greatly reduced induction of both DNA strand transfer activity and intragenic recombination between his1 heteroalleles. Spore viability is normal. These results suggest that DST1 is required for much of the observed induction of homologous recombination in S. cerevisiae during meiosis but not for normal sporulation.     

Evolutionary conservation of the spliceosomal protein, U2B''''.

U1 and U2snRNPs play key roles in pre-mRNA splicing. The interactions between the U1 and U2snRNP-specific proteins, U1A, U2A' and U2B' and their respective UsnRNAs are of interest both to elucidate their roles in splicing, and as models to study RNA-protein interactions. We have cloned a full-length cDNA, encoding U2B', from potato. This is the first report of a sequence for a plant UsnRNP protein. The plant U2B' sequence exhibits extensive similarity with the human U2B' protein at both the DNA and amino acid levels. The evolutionary conservation at the protein level, particularly in sequences implicated in determining specific binding to U2snRNA, suggests conservation of U2B' function from plants to man. The significance of amino acid substitutions in the RNP-80 motif with respect to U2snRNA binding in plants is discussed.     

Effect of RecF protein on reactions catalyzed by RecA protein.

RecF protein is one of at least three single strand DNA (ssDNA) binding proteins which act in recombination and repair in Escherichia coli. In this paper we show that our RecF protein preparation complexes with ssDNA so as to retard its electrophoretic movement in an agarose gel. The apparent stoichiometry of RecF-ssDNA-binding measured in this way is one RecF molecule for every 15 nucleotides and the binding appears to be cooperative. Interaction of the other two ssDNA-binding proteins, RecA and Ssb proteins, has been studied extensively; so in this paper we begin the study of the interaction of RecF and RecA proteins. We found that the RecF protein preparation inhibits the activity of RecA protein in the formation of joint molecules whether added before or after addition of RecA protein to ssDNA. It, therefore, differs from Ssb protein which stimulates joint molecule formation when added to ssDNA after RecA protein. We found that our RecF protein preparation inhibits two steps prior to joint molecule formation: RecA protein binding to ssDNA and coaggregate formation between ssDNA-RecA complexes and dsDNA. We found that it required a much higher ratio of RecF to RecA protein than normally occurs in vivo to inhibit joint molecule formation. The insight that these data give to the normal functioning of RecF protein is discussed.     

Dopamine acts through a D2-like receptor on a jellyfish motor neuron

Summary Dopamine, which is present in nerve-rich tissues of the hydromedusa Polyorchis penicillatus, produces membrane hyperpolarization in identified motor neurons from this jellyfish. In this study we demonstrate that the inhibitory action of dopamine is mediated by conventional drug-receptor interactions which are reversible, saturable and specific. When 10 M dopamine was applied by micro-spritzing onto voltage-clamped (holding potential, –20 mV), cultured swimming motor neurons, an outward current of about 1 nA was evoked. Using this technique, we established a potency order for several amines: dopaminenorepinephrine>tyramine >octopamine>-phenylethylamine. Dopamine is effective at concentrations betweeen 1 × 10^-8 and 1 × 10^-3 M. Several dopamine receptor blockers such as fluphenazine, haloperidol and spiperone reduced the dopamine-induced current in a concentration-dependent manner. Although propranolol, a -adrenergic blocker, reduced the dopamine response and SKF 83566, a D₁ blocker, increased the response, it appears that the dopamine receptors in these jellyfish neurons share pharmacological properties with mammalian D₂ dopamine receptors.     

The Maintenance of Single-Locus Polymorphism. I. Numerical Studies of a Viability Selection Model

The ability of viability selection to maintain single-locus polymorphism is investigated with two models in which the population is bombarded with a series of mutations with random fitnesses. In the first model, the population is allowed to reach equilibrium before mutation resumes; in the second the iterations and mutation occur simultaneously. Monte Carlo simulations of these models show that viability selection is easily able to maintain stable 6- or 7-allele polymorphisms and that monomorphisms and diallelic polymorphisms are uncommon. The question of how monomorphisms arise is also discussed.     

The Evolution of the Y Chromosome with X-Y Recombination

A theoretical population genetic model is developed to explore the consequences of X-Y recombination in the evolution of sex chromosome polymorphism. The model incorporates one sex-determining locus and one locus subject to natural selection. Both loci have two alleles, and the rate of classical meiotic recombination between the loci is r. The alleles at the sex-determining locus specify whether the chromosome is X or Y, and the alleles at the selected locus are arbitrarily labeled A and a. Natural selection is modeled as a process of differential viabilities. The system can be expressed in terms of three recurrence equations, one for the frequency of A on the X-bearing gametes produced by females, one for each of the frequency of A on the X- and Y-bearing gametes produced by males. Several special cases are examined, including X chromosome dominance and symmetric selection. Unusual equilibria are found with the two sexes having very different allele frequencies at the selected locus. A significant finding is that the allowance of recombination results in a much greater opportunity for polymorphism of the Y chromosome. Tighter linkage results in a greater likelihood for equilibria with a large difference between the sex chromosomes in allele frequency.     

Immunocytochemical localization of atrial natriuretic peptide in the venae cavae and the pulmonary veins of the rat

Summary In the present investigation atrial natriuretic peptide (ANP) was localized in striated myocytes of the venae cavae and the pulmonary veins in the rat by the use of immunohistochemical and immunocytochemical staining techniques. ANP was stored in granules which appeared to be morphologically similar to the atrial specific granules (ASG) of the atria. In general, the amount of ASG in the great thoracic veins was less than observed in the atria, and the specific granules appeared to be more evenly distributed throughout the sarcoplasm. However, the presence of ANP-containing specific granules in the venae cavae and the pulmonary veins may suggest participation of these veins in the production and secretion of the hormone.