Mutations upstream of the ribosome-binding site affect translational efficiency

The DNA coding for the major outer membrane lipoprotein of Escherichia coli has been fused to the coding region of the beta-galactosidase gene to measure the effect of various mutations on the efficiency of translation initiation. The various mutants were made by either inserting or deleting a small number of nucleotides into or from a region just upstream of the ribosome-binding site. These small mutations dramatically affect translation initiation as measured by the production of beta-galactosidase. We postulate that these mutations affect translation initiation by altering the secondary structure of the messenger RNA. In one case, we predict that a stem and loop just upstream of the Shine-Dalgarno sequence sterically hinders the binding of the ribosome to the mRNA.     

Amygdala kindled seizure stage is related to altered benzodiazepine binding site density

Benzodiazepine receptor binding was examined in rats at 3 stages of amygdaloid kindling (i.e., initial afterdischarge, Stage 3 and Stage 5) immediately or 24 hr after seizure. 3H-diazepam binding site density (Bmax) was significantly increased 24 hr after Stage 3 and Stage 5 kindled seizures in the hippocampus but not in the amygdala. There were no significant differences in the dissociation constants (KD) between kindled and control rats at any time point examined for either brain region. These results demonstrate that changes in benzodiazepine binding are observed with partial kindled seizures (i.e., Stage 3), indicating that generalized seizures are not prerequisite to increased benzodiazepine receptor site density.     

Dietary chloride as a determinant of disordered calcium metabolism in salt-dependent hypertension

In rats given desoxycorticosterone (DOC), the recently reported finding that a normal amount of dietary sodium chloride (NaCl) induces hypertension but an equimolar amount of sodium bicarbonate (NaHCO3) does not, might be a consequence of the differing effects of the two sodium salts on the metabolism of calcium. In accord with this hypothesis, we have found that, in uninephrectomized rats given DOC: Dietary NaCl induces persisting hypercalciuria and hypertension whereas an approximately equimolar amount of dietary NaHCO3 induces neither hypercalciuria nor hypertension. The urinary excretion of calcium becomes greater in rats given NaCl than in those given NaHCO3, before their blood pressures become different. Replacing dietary NaCl with a near equimolar amount of dietary NaHCO3 corrects both the hypercalciuria and the hypertension initially induced by NaCl.     

Methyl cinnamate derivatives enhance UV-induced mutagenesis due to the inhibition of DNA excision repair in Escherichia coli B/r

UV-induced mutagenesis in Escherichia coli B/r WP2 was enhanced by certain derivatives of methyl cinnamate which themselves were not mutagenic. Methyl ferulate, methyl isoferulate and methyl sinapate showed this effect markedly. Such an enhancement effect was absent with the derivatives of cinnamic acid and ethyl cinnamate and was not observed in Escherichia coli WP2s uvrA. Methyl sinapate also enhanced 4NQO-induced mutation and suppressed liquid-holding recovery in the above repair-proficient strain. The presence of methyl sinapate in plating agar medium decreased the survival of UV-irradiated cells of a recombination-repair-deficient strain, CM571 recA. However, the effect was not observed with those of WP2s uvrA. In an in vitro experiment in which the removal rate of thymine dimers was measured, methyl sinapate clearly inhibited this repair event. From these results, we conclude that methyl sinapate inhibits DNA excision repair, thus enhancing UV mutagenicity.     

Characteristics of major mutagenicity of instant coffee

Detailed quantitative studies on the mutagenicity of methylglyoxal showed that its contribution to the total mutagenicity of instant coffee on S. typhimurium TA100 was minor although we reported previously (Kasai et al., 1982) that its contribution to the mutagenicity of freshly brewed coffee was about 50%. Cysteine suppressed the mutagenicity of methylglyoxal and of methylglyoxal when added to instant coffee, but did not affect the mutagenicity of coffee itself. Catalase suppressed most of the mutagenicity of coffee, but not that of methylglyoxal or of methylglyoxal added to coffee.     

Activation of the food mutagens IQ and MeIQ by hepatic S9 fractions derived from various species

The ability of hepatic S9 mixes derived from different rodent species (rat, mouse, Syrian and Chinese hamster) to activate the mutagens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) was investigated using Salmonella typhimurium strain TA98. In general, the mutagenicity of IQ and MeIQ was greatest in the presence of S9 fractions from Swiss albino mice and least from fractions derived from Chinese hamsters. However, treatment of rats or hamsters with Aroclor 1254 had little or no effect on the activation of IQ or MeIQ to mutagens.     

The function of host discrimination and superparasitization in parasitoids

Summary Host discrimination, i.e. the ability to distinguish unparasitized hosts from parasitized ones, and to reject the latter for egg laying is present in many parasitic wasp species. This property is classically considered as an example of contest competition, and is supposed to have a number of functions. However, different species do not react to each other's marks and lay eggs in hosts parasitized by the other species. Apparently the marks used for recognition are specific.Multiparasitization is the best strategy when hosts are scarce and the egg supplies of the parasitoids are not limited. Interspecific host discrimination is not an ESS.Superparasitization within one species would have selective advantage if the number of unparasitized hosts is small and the wasp has a reasonable chance to lay her egg in a host that is not parasitized by herself, and if the chance for her offspring to survive the competitive battle with the first parasitoid larva is not too small. This is shown to be the case.However, marks are not individual and wasps cannot distinguish hosts parasitized by themselves from those parasitized by others. The hypothesis is tested that the egg laying strategy (i.e. the decision to superparasitize) of wasps is dependent on the number of conspecifics that is searching simultaneously for hosts, since this determines the chance that a parasitized host encountered by a wasp is parasitized by herself.It is shown that host discrimination cannot be regarded as a case of contest competition. Other aspects of superparasitization, related to interference and population regulation, sex allocation and encapsulation are briefly discussed.     

Sex ratio and intrasexual kin competition in mammals

Summary Asymmetries in both intrasexual competition and generation overlap occur in Antechinus (Dasyuridae; Marsupialia). We show that the range of interpopulation variation in the sex ratio of pouch young spans and exceeds the range of sex ratios at birth hitherto recorded from eutherians (Clutton-Brock and Albon 1983). Although postweaning dispersal and male mortality are similar among all Antechinus populations, interpopulation variance in female longevity leads to variable duration of mother/daughter interaction. As this duration increases, parental investment is increasingly biased toward males, supporting the view that local competition among female kin for resources may influence mammalian sex ratios.     

Fatness, menarche, and female fertility

It is hypothesized that a particular ratio of fat to lean mass is required for menarche and the maintenance of regular menstrual cycles. Females who lose 10-15% of normal weight for height, equivalent to a loss of 1/3 of body fat, become amenorrheic, presumably due to hypothalamic dysfunction. Adipose tissue may provide signals to the central nervous system and gonadotropin regulatory areas either directly, by estrogen production, or indirectly, by the effects of relative fatness on temperature control and metabolic rate, or by both means. Women with hypothalamic dysfunction experience changes in the secretion of gonadotropins, luteinizing hormone, follicle-stimulating hormone, and estrogen. Weight gain restores postmenarcheal secretion patterns. This approach suggests that the secular trend toward earlier age at menarche reflects earlier attainment of critical weight as a result of improved nutrition and child care. In many societies, subnutrition may explain the observed submaximum fertility. This suggests a need to integrate family planning programs with nutrition programs in many developing countries. It is important to note that the prediction of the minimum weight for height for onset and maintenance of ovulatory cycles is from total water as percentage of body weight. Although the percentage of fat in the body is inversely related to the percent of body water, only the latter is predictive. Successful prediction of the minimum weights for height is related to a lean mass/fat ratio represented by about 17% fat of body weight at menarche and 22% of body weight at the completion of growth at age 18 years.