NUCLEAR DNA CONTENT IN POPULATIONS OF PINUS RIGIDA

Five populations of Pinus rigida growing in contrasting ecological situations ranging from North Carolina (35°53'N latitude) to Quebec (45°06'N latitude) showed no significant variation in amounts of nuclear DNA with respect to germinating seedlings. Nuclear volume of dormant nuclei also showed no significant variation between and within populations, a finding that is consistent with the concept that the basic 2C DNA value of Pinus rigida is uniform under all habitats. This finding is in contrast to numerous reports for other coniferous species.     

Solid-state 15N NMR of oriented lipid bilayer bound gramicidin A'

Highly oriented samples of lipid and gramicidin A' (8:1 molar ratio) have been prepared with the samples extensively hydrated (approximately 70% water v/w). These preparations have been shown to be completely in a bilayer phase with a transition temperature of 28 degrees C, and evidence is presented indicating that the gramicidin is in the channel conformation. An estimate of the disorder in the alignment of the bilayers parallel with the glass plates used to align the bilayers can be made from the asymmetry of the nuclear magnetic resonances (NMR). Such an analysis indicates a maximal range of disorder of +/- 3 degrees. Uniformly 15N-labeled gramicidin has been biosynthesized by Bacillus brevis grown in a media containing 15N-labeled Escherichia coli cells as the only nitrogen source. When prepared with labeled gramicidin, the oriented samples result in high-resolution 15N NMR spectra showing 12 resonances for the 20 nitrogen sites of the polypeptide. The frequency of the three major multiple resonance peaks has been interpreted to yield the approximate orientation of the N-H bonds in the peptide linkages with respect to the magnetic field. These bond orientations are only partially consistent with the extant structural models of gramicidin.     

Expanded thermal niche for a diving vertebrate: A leatherback turtle diving into near-freezing water

The global distribution of extant reptiles is more limited than that of mammals or birds, with low reptilian species diversity at high latitudes. Central to this limited geographical distribution is the ectothermic nature of reptiles, which means that they generally become torpid at cold temperatures. However, here we report the first detailed telemetry from a leatherback turtle (Dermochelys coriacea) diving in cold water at high latitude. An individual equipped with a satellite tag that relayed temperature-depth profiles dived continuously for many weeks into sub-surface waters as cold as 0.4 °C. Global warming will likely increase the foraging range of leatherback turtles further into temperate and boreal waters.     

Frequency-dependent conspecific attraction to food patches

In many ecological situations, resources are difficult to find but become more apparent to nearby searchers after one of their numbers discovers and begins to exploit them. If the discoverer cannot monopolize the resources, then others may benefit from joining the discoverer and sharing their discovery. Existing theories for this type of conspecific attraction have often used very simple rules for how the decision to join a discovered resource patch should be influenced by the number of individuals already exploiting that patch. We use a mechanistic, spatially explicit model to demonstrate that individuals should not necessarily simply join patches more often as the number of individuals exploiting the patch increases, because those patches are likely to be exhausted soon or joining them will intensify future local competition. Furthermore, we show that this decision should be sensitive to the nature of the resource patches, with individuals being more responsive to discoveries in general and more tolerant of larger numbers of existing exploiters on a patch when patches are resource-rich and challenging to locate alone. As such, we argue that this greater focus on underlying joining mechanisms suggests that conspecific attraction is a more sophisticated and flexible tactic than currently appreciated.     

Diet changes in the carbon and nitrogen content of the copepod Metridia lucens

Diel changes in the near-surface (0–50 m) abundance, prosomelength, and carbon and nitrogen content of the copepod Metridialucens were measured in Deep Cove, Doubtful Sound, New Zealand(45°27'S, 167°9'E) between 3 and 6 September 1996. Metridialucens showed maximal abundance a night, suggesting a patternof normal diel vertical migration (DVM). The change in abundancesuggested that the descent of the population occurred –1h prior to dawn and the ascent –1 h after dusk. However,a proportion of the population remained near the surface duringthe day. Although there was no diel pattern in the prosome lengthof M.lucens collected near the surface, there was a marked dielcycle in the measured carbon and nitrogen contents, with maximalvalues being measured towards the end of the night prior tothe downward migration. We suggest that this diet cycle in themeasured elemental content was caused by DVM occurring morestrongly in those animals which had a better body condition,i.e. a higher elemental content per unit length.     

Molecular cloning of cis-acting regulatory alleles of the Bacillus subtilis amyR region by using gene conversion transformation.

Three cis-acting alleles (gra-10, gra-5, and amyR2) of the Bacillus subtilis amyR promoter locus each cause catabolite repression-resistance of amyE-encoded alpha-amylase synthesis. The gra-10, gra-5, and amyR2 alleles were transferred from the chromosomes of their respective hosts to a plasmid carrying the amyR1-amyE+ gene by the process of gene conversion which is carried out during transformation of competent B. subtilis by plasmid clones carrying homologous DNA. The cloned amyR promoter regions containing the gra-10 and gra-5 mutations were shown to confer catabolite repression-resistance in cis to the synthesis of chloramphenicol acetyltransferase encoded by the cat-86 indicator gene when subcloned into the promoter-probe plasmid pPL603B. Implications concerning both the regulation of amyR utilization and the process of gene conversion in B. subtilis are discussed.     

Analysis of DNA adducts by accelerator mass spectrometry in human breast tissue after administration of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and benzo[a]pyrene

Epidemiological evidence has suggested an association between meat consumption and the risk of breast cancer. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic amine found in cooked meat, has been implicated in the aetiology of breast cancer and has been shown to induce tumour formation in rodent mammary glands. In addition, polycyclic aromatic hydrocarbons, such as benzo[a]pyrene (B[a]P) which has also been shown to induce tumour formation at a number of sites in rodents including the breast, are produced during the cooking of meat through the pyrolysis of fats. The aim of this study was to examine the bioavailability of these compounds to human breast tissue and their ability to bind to DNA to form DNA adducts. Patients undergoing breast surgery at York District Hospital were orally administered prior to surgery a capsule containing 20 μg of ¹⁴C PhIP (182 kBq, specific activity 2.05 GBq/mmol) or 5 μg of ¹⁴C B[a]P (36 kBq, specific activity 1.81 GBq/mmol). At surgery, normal and tumour breast tissue was resected and tissue concentrations of carcinogen measured by liquid scintillation counting and DNA adduct levels by accelerator mass spectrometry (AMS) were subsequently determined. It was found that both ¹⁴C PhIP and ¹⁴C B[a]P were able to reach the target organ where they had the ability to form DNA adducts. The level of adducts ranged from 26.22–477.35 and 6.61–208.38 adducts/10¹² nucleotides following administration of ¹⁴C PhIP and ¹⁴C B[a]P, respectively, with no significant difference observed between levels in normal or tumour tissue. In addition, the data obtained in this study were comparable to adduct levels previously found in colon samples following administration of the same compounds to individuals undergoing colorectal surgery. This is the first report that these two carcinogens bind to human breast DNA after administration of a defined low dose.     

Single copy DNA homology in sea stars

Summary The sequence homology in the single copy DNA of sea stars has been measured. Labeled single copy DNA fromPisaster ochraceus was reannealed with excess genomic DNA fromP. brevispinus, Evasterias troschelii, Pycnopodia helianthoides, Solaster stimpsoni, andDermasterias imbricata. Reassociation reactions were performed under two criteria of salt and temperature. The extent of reassociation and thermal denaturation characteristics of hybrid single copy DNA molecules follow classical taxonomic lines.P. brevispinus DNA contains essentially all of the sequences present inP. ochraceus single copy tracer whileEvasterias andPycnopodia DNAs contain 52% and 46% of such sequences respectively. Reciprocal reassociation reactions with labeledEvasterias single copy DNA confirm the amount and fidelity of the sequence homology. There is a small definite reaction of uncertain homology betweenP. ochraceus single copy DNA andSolaster orDermasterias DNA. SimilarlySolaster DNA contains sequences homologous to approximately 18% ofDermasterias unique DNA. The thermal denaturation temperatures of heteroduplexes indicate that the generaPisaster andEvasterias diverged shortly after the divergence of the subfamilies Pycnopodiinae and Asteriinae. The twoPisaster species diverged more recently, probably in the most recent quarter of the interval since the separation of the generaPisaster andEvasterias.