Regulation of Escherichia coli secA mRNA translation by a secretion-responsive element.

The Escherichia coli secA gene, whose translation is responsive to the proficiency of protein export within the cell, is the second gene in a three-gene operon and is flanked by gene X and mutT. By using gene fusion and oligonucleotide-directed mutagenesis techniques, we have localized this translationally regulated site to a region at the end of gene X and the beginning of secA. This region has been shown to bind SecA protein in vitro. These studies open the way for a direct investigation of the mechanism of secA regulation and its coupling to the protein secretion capability of the cell.     

Displacement of hepatic ornithine carbamoyltransferase from mitochondria to cytosol in Reye's syndrome.

In two patients with fatal Reye's Syndrome, total ornithine carbamoyltransferase (OCTase) activity in the liver was 50 and 75% of that found in three control livers. The levels of enzymatic activity would not be expected to have resulted in the 7- and 17-fold elevations in plasma ammonia levels found in the patients. Levels of 47 and 60% of the OCTase activity, however, were found in the cytosolic fraction compared to an average of 7% for control livers. Thus, the amount of enzymatic activity in the mitochondrial fractions was only 20 and 30% of that found in control mitochondrial fractions. This study suggests that, if only mitochondrial OCTase is active in the urea cycle, the decreases in functional enzyme found in Reye's Syndrome may be considerably greater than that reflected in total enzyme assays.     

Molecular mapping of the mouse ob mutation.

The mouse ob mutation has been mapped relative to a series of RFLPs among the progeny of three separate mouse crosses: an intraspecific backcross, an intraspecific intercross, and an interspecific intercross. Genotypic assignment at the ob locus was made by making use of measurements of body mass index and the plasma concentrations of glucose and insulin. These data have suggested that the development of diabetes in these animals is a consequence of unlinked polygenes. There was also evidence that unlinked Mus spretus alleles can diminish the obesity of ob/ob mice. From these data we have mapped several markers on chromosome 6 with the following order: cen-Cola-2-Met-ob-Cpa-Tcrb. The homologs of markers that flank ob map to human chromosome 7q, suggesting that if there is a human homologue of ob, it maps to 7q31.     

The reproductive behavior of six species of Namib desert tenebrionid beetles (Coleoptera: Tenebrionidae)

The reproductive behavior of six species of tenebrionid beetles (Coleoptera: Tenebrionidae) was studied in the Namib Desert of southern Africa. In three species, males follow closely behind females (following behavior), while in the other three species, males mount females and remain clasped to them for extended periods (riding behavior). Following behavior occurs before and sometimes after copulation, while riding behavior occurs primarily after copulation. Males of all six species guard females from contesting males, although the effectiveness of guarding is greater in riding species. The evolution of the two male mating strategies does not appear to be related to operational sex ratio differences but, rather, to differential tendencies of females to remate. Variation in total pair duration within following and riding species may be attributed partly to species differences in operational sex ratio. However, pair durations are not affected by experimental manipulations of sex ratio in each species.     

Oviposition by screwworm flies (Diptera: Calliphoridae) on contact with host fluids

Factor affecting oviposition by screwworm flies, Cochliomyia hominivorax (Coquerel), contacting different host fluids were examined in a laboratory bioassay. Fresh bovine blood, which does not release the attractive odors involved in host finding, nevertheless stimulated as many or more females to oviposit than did the other fluids tested. These other fluids included attractive fluid from screwworm-infected wounds (a favored oviposition site in nature) and cultures of Providencia rettgeri (a bacterium implicated in attractant production). Oviposition did not vary with batch of fresh blood or frozen storage, making blood a useful standard for comparing oviposition rates among studies. Oviposition did vary with the substrate to which the blood was applied, suggesting that an interaction between tactile and chemical stimuli is important for host recognition. Both insemination and darkness during bioassay increased oviposition rates, but the magnitude of these effects was small compared with that due to substrate. Age had no effect for at least 1 wk after females became gravid.     

Phylogenetic relationships among four members of Stizostedion (Percidae) determined by mitochondrial DNA and allozyme analyses

Phylogenetic relationships among four Stizostedion species were examined using mitochondrial DNA (mtDNA) and allozyme analyses. Twenty-six allozyme loci were scored, and mtDNA variation was examined using 24 restriction endonucleases, yielding 48–57 restriction sites among the species. Genetic distance analyses show that the two North American species ( S. canadense and S. vitreum ) cluster in one group, while the two European species ( S. hciopercu and S. vogense ) form a second group. Nei's genetic distance between these two groups was 0.7 ± 0.2 for allozymes, while the corresponding mtDNA sequence divergence was 14.8 ± 2.0%, suggesting that these two groups diverged approximately 10 million years ago. Thus, these data are consistent with the hypothesis that Stizostedion colonized North America during the Pliocene.     

Triterpenoid saponins from Medicago hispida.

Soyasaponin III has been characterized and the structure of a new triterpenoid saponin, hispidacin, has been elucidated as soyasapogenol B-3-O-alpha-L-rhamnopyranopyranosyl(1----2)- beta-D-glucopyranosyl(1----2)-beta-D-glucuronopyranoside by a combination of fast-atom bombardment mass spectrometry, 13C NMR spectroscopy, and some chemical transformations. Mechanism of transformation of soyasapogenol B to soyasapogenols D, and F has also been rationalized.     

Pyridostigmine enhances even if it does not normalize the growth hormone responses to growth hormone-releasing hormone in patients with Cushing's disease.

Subjects with Cushing's disease have diminished growth hormone (GH) response to growth hormone-releasing hormone (GHRH). The aim of our study was to investigate the underlying mechanism of this diminished GH response in these patients using pyridostigmine (PD), an acetylcholinesterase inhibitor, which is reported to increase GH secretion by reducing somatostatin tone. Eight subjects with untreated Cushing's disease (caused by a pituitary adenoma) and 6 control subjects received GHRH 100 micrograms in 1 ml of saline, as intravenous bolus injection 60 min after (1) placebo (2 tablets, p.o.) or (2) PD (120 mg, p.o.). After GHRH plus placebo, the GH peak (mean +/- SEM) was significantly lower in subjects with Cushing's disease (2.4 +/- 0.5 micrograms/l) compared to control subjects (25.1 +/- 1.8 micrograms/l, p less than 0.05). After GHRH plus PD, the GH peak was significantly enhanced both in subjects with Cushing's disease (7.1 +/- 2.3 micrograms/l, p less than 0.05) and in control subjects (42.3 +/- 4.3 micrograms/l, p less than 0.05). In patients with Cushing's disease, the GH response to GHRH plus PD was lower with respect to the GH response to GHRH alone in normal subjects. We conclude that hypercortisolism may cause a decrease in central cholinergic tone which is in turn hypothesized to be responsible of an enhanced somatostatin release from the hypothalamus. However, other metabolic or central nervous system alterations may act synergistically with hypercortisolism in causing GH inhibition in patients with Cushing's disease.