Muscle-specific gene expression controlled by a regulatory element lacking a MyoD1-binding site

Muscle-specific expression of the gene encoding the delta subunit of the acetylcholine receptor is controlled by a 54-base-pair region that does not contain a binding site for MyoD1, a protein involved in activation of the myogenic program. A MyoD1-binding site is present in the proximal promoter region of the gene encoding the delta-subunit, but is neither sufficient nor necessary for muscle-specific expression in transfected muscle cells.     

Tests of the helix dipole model for stabilization of alpha-helices

Charged groups play a critical role in the stability of the helix formed by the isolated C-peptide (residues 1-13 of ribonuclease A) in aqueous solution. One charged-group effect may arise from interactions between charged residues at either end of the helix and the helix dipole. We report here that studies of C-peptide analogues support the helix dipole model, and provide further evidence for the importance of electrostatic interactions not included in the Zimm-Bragg model for alpha-helix formation.     

Four-terminal resistance of a ballistic quantum wire

The electrical resistance of a conductor is intimately related to the relaxation of the momentum of charge carriers. In a simple model, the accelerating force exerted on electrons by an applied electric field is balanced by a frictional force arising from their frequent collisions with obstacles such as impurities, grain boundaries or other deviations from a perfect crystalline order. Thus, in the absence of any scattering, the electrical resistance should vanish altogether. Here, we observe such vanishing four-terminal resistance in a single-mode ballistic quantum wire. This result contrasts the value of the standard two-probe resistance measurements of h/2e2 approximately 13 kOmega. The measurements are conducted in the highly controlled geometry afforded by epitaxial growth onto the cleaved edge of a high-quality GaAs/AlGaAs heterostructure. Two weakly invasive voltage probes are attached to the central section of a ballistic quantum wire to measure the inherent resistance of this clean one-dimensional conductor.     

"Curing" of Nicotiana attenuata leaves by small mammals does not decrease nicotine contents

Basal leaves of Nicotiana attenuata are frequently found neatly excised at the petiole and piled on rocks or soil in the sun until dry, after which they disappear, sometimes to be found again in the nests of Neotoma lepida . In response to herbivore attack, N. attenuata increases the concentration of nicotine in its leaves, where it functions as an induced defense. Since excision of leaves at the petiole allows for leaf removal without substantially activating this induced defense, and air-drying at high temperatures can volatilize nicotine, we examined the hypothesis that the observed leaf ""curing"" behavior decreased nicotine contents. In a natural population, replicate bundles of excised leaves were allowed to dry in the sun for up to 96 hours and harvested in 10 intervals. Even though surface temperatures reached 63° C during drying, no significant loss of nicotine was observed. In the laboratory, significant losses of nicotine were not observed until leaves were dried at 100° C. Nicotine contents of naturally ""cured"" leaf piles at 4 populations were found to be marginally higher than those of neighboring intact plants from which the leaves were likely harvested. We conclude that mammalian ""curing"" behavior does not reduce nicotine contents and may allow the leaves to be used for insect repellant purposes.     

Denning chronology of black bears in eastern Rocky Mountain National Park, Colorado

Understanding factors influencing the timing of den entrance and emergence of black bears ( Ursus americanus ) provides insight for bear management. We determined den entrance and emergence dates for bears in Rocky Mountain National Park (RMNP) and related these dates to vegetative productivity, weather, habitat, and demographic factors to assess the influence of these factors on denning chronology. Date of den entrance was most strongly influenced by age class, precipitation, and proportion of human-use areas in annual home ranges. Den entrance was typically later for adult bears during wetter years and when annual home ranges contained a greater proportion of human-use areas. Sex and presence of human-use areas were most strongly related to den emergence. Male bears typically emerged from dens before females, and bears emerged from dens earlier when human-use areas composed a greater proportion of annual home ranges. Collectively, our results suggest that denning behavior of black bears in RMNP was strongly influenced by presence of human-use areas, likely because of foods associated with such areas. Managers of black bears in RMNP can use precipitation to predict relative dates of den entrance, thereby allowing for more efficient strategies to combat potentially negative human–black bear encounters.     

Amyloid precursor protein and its homologues: a family of proteolysis-dependent receptors

The Alzheimer’s amyloid precursor protein (APP) belongs to a conserved gene family that also includes the mammalian APLP1 and APLP2, the Drosophila APPL, and the C. elegans APL-1. The biological function of APP is still not fully clear. However, it is known that the APP family proteins have redundant and partly overlapping functions, which demonstrates the importance of studying all APP family members to gain a more complete picture. When APP was first cloned, it was speculated that it could function as a receptor. This theory has been further substantiated by studies showing that APP and its homologues bind both extracellular ligands and intracellular adaptor proteins. The APP family proteins undergo regulated intramembrane proteolysis (RIP), generating secreted and cytoplasmic fragments that have been ascribed different functions. In this review, we will discuss the APP family with focus on biological functions, binding partners, and regulated processing.     

Antihypertensive and cardiac effects of two novel beta-adrenoceptor blocking drugs.

Two new beta-adrenoceptor blocking drugs with acute antihypertensive and positive inotropic effects are described: Compound A (2-[4-(3-tert.butylamino-2-hydroxypropoxy)phenyl]-4-trifluoromethylimidazole) and MK-761 (2-(3-tert.butylamine-2-hydroxypropoxy)-3-cyanopyridine hydrochloride). In SH rats both compounds, given orally, lowered arterial pressure and were more potent than hydralazine. The antihypertensive effect of compound A but not of MK-761 was antagonized by timolol. Both compounds had positive inotropic activity on cat heart papillary muscles; these effects were antagonized by timolol. The pretreatment of animals with reserpine greatly reduced the positive inotropic effect of MK-761 but not of compound A. The acute antihypertensive and positive inotropic effects of compound A are like to be at least partially due to stimulation of beta-adrenoceptors, e.g. intrinsic sympathomimetic activity. The effects of MK-761 on the same parameters appear to be mediated by different mechanisms.     

Antihypertensive and other cardiovascular effects of 2-(3-pyridyl)- and 2-(4-pyridyl)-4-trifluoromethylimidazoles

Summary 2 new 4-trifluoromethylimidazole derivatives were found which lowered mean arterial pressure in renal and spontaneously hypertensive (SH) rats by the oral route. In SH rats, compounds A and B were 0.1 and 0.3 times, respectively, as potent as hydralazine. No tolerance development was observed in SH rats with either compound over a 1-week period. In anesthetized dogs, both compounds lowered arterial pressure and peripheral vascular resistance but increased cardiac output. By intraarterial administration, both compounds increased femoral arterial blood flow. These findings represent discovery of a new class of vasodilator drugs.Deceased, May 31, 1978.