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.     

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.     

Isolation and characterization of folded fragments released by Staphylococcal aureus proteinase from the non-histone chromosomal protein HMG-1

HMG-1 was isolated from newborn calf thymus without exposure to overt denaturing conditions. The purified protein was digested under several solvent conditions with the proteinase (endoproteinase GluC) from Staphylococcus aureus strain V8. We found that the preferred site of attack by the enzyme on HMG-1 was influenced markedly by ionic strength and temperature. In 0.35 M NaCl/50 mM Tris-phosphate (pH 7.8) at 37 degrees C, cleavage near the junction between the A and B domains is predominant, as previously reported by Carballo et al. (EMBO J. 2 (1983) 1759-1764). However, in 50 mM Tris-phosphate (pH 7.8) lacking NaCl and at 0 degrees C, cleavage between the B and C domains strongly predominates. Three major products of the digestions were purified and characterized. The fragment consisting of domains B and C was found by circular dichroism to contain a substantial amount of helix. This re-emphasizes the importance of avoiding overt denaturing conditions when working with members of the HMG-1 family.     

Action of a cell wall proteinase from Lactococcus lactis subsp. cremoris SK11 on bovine α s1-casein

Summary The cell wall-associated proteinase from Lactococcus lactis subsp. cremoris SK11 was partially purified and incubated with _s1-casein for various times up to 48 h. Sixteen trifluoroacetic acid-soluble oligopeptide hydrolysis products were identified by determination of the aminp acid sequence. Eleven of these oligopeptides originated from the 78-residue sequence comprising the C-terminal region of _s1-casein and were present among the products after the first 60 min of digestion. Three oligopeptides from the N-terminal region and two others from the central region of the _s1-casein sequence were also present among the early digestion products although in smaller amounts than most of the oligopeptides from the C-terminal region. No cleat consensus sequence of amino acid residues surrounding the cleavage sites could be identified.Offprint requests to: G. G. Pritchard     

The use of field-inversion gel electrophoresis for deletion detection in Duchenne muscular dystrophy.

Deletion is a common cause of Duchenne muscular dystrophy (DMD). Field-inversion gel electrophoresis, in conjunction with Southern blot hybridization, was used to detect large SfiI DNA fragments in the DMD locus. Two unrelated boys with DMD were found to have abnormal sized DNA fragments resulting from deletions. Some of the female relatives of these patients were also shown by this method to have deletions in the DMD locus.     

Beta-adrenergic agents increase the phosphorylation of phosphofructokinase in isolated rat epididymal white adipose tissue.

Pieces of rat epididymal adipose tissue were incubated in medium containing [32P]phosphate for 2 h to achieve steady-state labelling of intracellular phosphoproteins and then with or without hormones for a further 15 min. Phosphofructokinase was rapidly isolated from the tissue by use of either Blue Dextran-Sepharose chromatography or immunoprecipitation with antisera raised against phosphofructokinase purified from rat interscapular brown adipose tissue. Similar extents of incorporation of 32P into phosphofructokinase were measured by both techniques. Exposure of the tissue to adrenaline or the beta-agonist isoprenaline increased phosphorylation by about 5-fold (to about 1.4 mol of phosphate/mol of enzyme tetramer). No change in phosphorylation was detected with the alpha-agonist phenylephrine, but exposure to insulin resulted in an approx. 2-fold increase. The increased phosphorylation observed with isoprenaline was found to be associated with a decrease in the apparent Ka for fructose 2,6-bisphosphate similar to that observed on phosphorylation of phosphofructokinase purified from rat epididymal white adipose tissue with the catalytic subunit of cyclic AMP-dependent protein kinase. These results support the view [Sale & Denton (1985) Biochem. J. 232, 897-904] that an increase in cyclic AMP in adipose tissue may result in an increase in glycolysis through the phosphorylation of phosphofructokinase by cyclic AMP-dependent protein kinase.