The effects of salicylic acid on metabolism and potassium ion content in yeast.

Under anaerobic conditions, at low pH and 30 degrees, commercial baker's yeast loses K+ ion in the presence of salicylic acid. Glucose utilization is inhibited. In suspensions containing no glucose, carbohydrate stores of the cell are dissimilated to carbon dioxide and alcohol. The ion loss and inhibitory effects of salicylic acid on glucose utilization are reversed by washing the cells free of salicylate. The loss of K+ appears to be due at least partly to a K+-H+ exchange process. An unexplained maximum is seen in the curves of either net K+ loss or K+ efflux versus salicylic acid concentration. At 6 degrees the effects of salicylic acid on both endogenous metabolism and net K+ loss are minimal. Furthermore, no maximum is seen in the K+ loss-salicyclic concentration curve at this temperature. It is generalized that salicylic acid or salicylate may elicit K+ leakage from many types of cells, i.e., a fundamental action of this compound may be its ability to affect (reduce) K+ content of the cell; furthermore, it appears that the salicylate effects on K+ loss may be associated in an as-yet-unknown manner with the metabolic effects of this compound. The effects of salicylate on K+ loss in yeast may not be unique for this compound, since no experiments of this nature have been done with other penetrating undissociated acids.     

Hand temperature norms for headache, hypertension, and irritable bowel syndrome

Hand temperature norms are presented for 221 headache patients (migraine, mixed, and tension), 105 hypertensives, 45 irritable bowel syndrome patients, and 56 normal controls under conditions of resting baseline, self-relaxation, volitional handwarming, mental arithmetic, and cold pressor. The two vascular headache groups (migraine and mixed) had significantly lower hand temperatures across conditions.     

Linear molecules of tobacco ptDNA end at known replication origins and additional loci

Higher plant plastid DNA (ptDNA) is generally described as a double-stranded circular molecule of the size of the monomer of the plastid genome. Also, the substrates and products of ptDNA replication are generally assumed to be circular molecules. Linear or partly linear ptDNA molecules were detected in our present study using pulsed-field gel electrophoresis and Southern blotting of ptDNA restricted with ‘single cutter’ restriction enzymes. These linear DNA molecules show discrete end points which were mapped using appropriate probes. One possible explanation of discrete ends would be that they represent origins of replication. Indeed, some of the mapped ends correlate well with the known origins of replication of tobacco plastids, i.e. both of the oriA sequences and—less pronouncedly—with the oriB elements. Other ends correspond to replication origins that were described for Oenothera hookeri, Zea mays, Glycine max and Chlamydomonas reinhardtii, respectively, while some of the mapped ends were not described previously and␣might therefore represent additional origins of replication.     

Extracting gene networks for low-dose radiation using graph theoretical algorithms

Genes with common functions often exhibit correlated expression levels, which can be used to identify sets of interacting genes from microarray data. Microarrays typically measure expression across genomic space, creating a massive matrix of co-expression that must be mined to extract only the most relevant gene interactions. We describe a graph theoretical approach to extracting co-expressed sets of genes, based on the computation of cliques. Unlike the results of traditional clustering algorithms, cliques are not disjoint and allow genes to be assigned to multiple sets of interacting partners, consistent with biological reality. A graph is created by thresholding the correlation matrix to include only the correlations most likely to signify functional relationships. Cliques computed from the graph correspond to sets of genes for which significant edges are present between all members of the set, representing potential members of common or interacting pathways. Clique membership can be used to infer function about poorly annotated genes, based on the known functions of better-annotated genes with which they share clique membership (i.e., “guilt-by-association”). We illustrate our method by applying it to microarray data collected from the spleens of mice exposed to low-dose ionizing radiation. Differential analysis is used to identify sets of genes whose interactions are impacted by radiation exposure. The correlation graph is also queried independently of clique to extract edges that are impacted by radiation. We present several examples of multiple gene interactions that are altered by radiation exposure and thus represent potential molecular pathways that mediate the radiation response.     

A role for Mlh3 in somatic hypermutation

Somatic hypermutation (SHM) and class switch recombination (CSR) allow B cells to make high affinity antibodies of various isotypes. Both processes are initiated by activation-induced cytidine deaminase (AID) to generate dG:dU mismatches in the immunoglobulin genes that are resolved differently in SHM and CSR to introduce point mutations and recombination, respectively. The MutL homolog MLH3 has been implicated in meiosis and DNA mismatch repair (MMR). Since it interacts with MLH1, which plays a role in SHM and CSR, we examined these processes in Mlh3-deficient mice. Although deficiencies in other MMR proteins result in defects in SHM, Mlh3(-/-) mice exhibited an increased frequency of mutations in their immunoglobulin variable regions, compared to wild type littermates. Alterations of mutation spectra were observed in the Jh4 flanking region in Mlh3(-/-) mice. Nevertheless, Mlh3(-/-) mice were able to switch to IgG3 or IgG1 with similar frequencies to control mice. This is the first instance where a loss of a DNA repair protein has a positive impact on the rate of SHM, suggesting that Mlh3 normally inhibits the accumulation of mutations in SHM.     

Somatic cell genetics of immunoglobulin production

Tissue culture lines of mouse myeloma cells have been used to study the somatic cell genetics of immunoglobulin production. Assays have been developed to identify and quantify mutants that have undergone changes in either the synthesis or structure of the immunoglobulin molecule. All of the classical types of mutants have been identified. What is unusual is that these mutants arise at a very high frequency. This genetic instability seems to be restricted to immunoglobulin genes. The fusion of mutant and wild-type cells allows the study of interaction of genes and gene products.