Radiohalos in coalified wood: new evidence relating to the time of uranium introduction and coalification.

The discovery of embryonic halos around uranium-rich sites that exhibit very high (238)U/(206)Pb ratios suggests that uranium introduction may have occurred far more recently than previously supposed. The discovery of (210)Po halos derived from uranium daughters, some elliptical in shape, further suggests that uranium-daughter infiltration occurred prior to coalification when the radionuclide transport rate was relatively high and the matrix still plastically deformable.

Characterization of an episome produced in hamster cells that amplify a transfected CAD gene at high frequency: functional evidence for a mammalian replication origin.

In a previous study (G. M. Wahl, B. Robert de Saint Vincent, and M. L. De Rose, Nature (London) 307:516-520, 1984), we used gene transfer of a CAD cosmid to demonstrate that gene position profoundly affects amplification frequency. One transformant, T5, amplified the donated CAD genes at a frequency at least 100-fold higher than did the other transformants analyzed. The CAD genes in T5 and two drug-resistant derivatives were chromosomally located. In this report, we show that a subclone of T5 gives rise to an extrachromosomal molecule (CAD episome) containing the donated CAD genes. Gel electrophoresis indicated that the CAD episome is approximately 250 to 300 kilobase pairs, and a variety of methods showed that it is a covalently closed circle. We show that the CAD episome replicates semiconservatively and approximately once per cell cycle. Since the CAD cosmid, which comprises most of the CAD episome, does not replicate autonomously when transfected into cells, our results indicate that either the process which generated the episome resulted in a cellular origin of DNA replication being linked to the CAD sequences or specific rearrangements within the episome generated a functional origin. The implications of these results for mechanisms of gene amplification and the genesis of minute chromosomes are discussed.

Clinical decision-making with treadmill testing and thallium 201.

Fifty patients were prospectively evaluated for myocardial ischemia utilizing treadmill testing and thallium-201 imaging. By coronary angiography, 43 had significant coronary stenosis and seven were normal. The sensitivity, specificity, accuracy and predictive value of treadmill testing alone (81 per cent, 71 per cent, 80 per cent and 95 per cent) did not statistically differ from that of thallium-201 imaging (70 per cent, 86 per cent, 72 per cent and 97 per cent). Combined treadmill testing and thallium-201 imaging (84 per cent, 71 per cent, 80 per cent and 98 per cent) did not significantly affect the results of treadmill testing alone. Thallium-201 imaging failed to identify a number of patients with high risk lesions. The high prevalence of disease, the presentation of typical angina, preselection bias, multiple lead monitoring and exclusion of patients with abnormalities on the resting electrocardiogram probably accounted for failure of thallium-201 imaging to improve the results obtained with treadmill testing. The use of thallium-201 imaging in certain subsets of patient (resting electrocardiographic abnormalities, nondiagnostic treadmill testing, atypical chest pain or asymptomatic patients with abnormalities on treadmill testing) may be of value. However, the use of thallium-201 imaging as a routine screening procedure for myocardial ischemia in patients with typical angina, without due consideration of the prevalence of the disease in the population, is not justified.

Specificity of CNS and PNS regulatory subelements comprising pan-neural enhancers of the deadpan and scratch genes is achieved by repression.

The Drosophila pan-neural genes deadpan (dpn) and scratch (scrt) are expressed in most or all developing neural precursor cells of the central nervous system (CNS) and peripheral nervous system (PNS). We have identified a cis-acting enhancer element driving full pan-neural expression of the dpn gene which is composed of independent CNS- and PNS-specific subelements. We have also identified CNS- and PNS-specific subelements of the scrt enhancer. Deletion analysis of the dpn and scrt PNS-specific subelements reveals that PNS specificity of these two evolutionarily unrelated enhancers is achieved in part by repression of CNS expression. We discuss the implications of the striking organizational similarities of the dpn, scrt, and sna pan-neural enhancers.

Effects of acute alcohol administration on propranolol absorption.

Alterations in propranolol absorption secondary to concomitant ethanol administration was investigated in five normal adults. With alcohol administration, there was an increase in the area under the plasma concentration-time curve (AUC) and maximum plasma concentration (CPmax). Ethanol caused a decrease in the rate of absorption and an increase in the rate of elimination of propranolol. It appears that the acute, concomitant administration of alcohol with propranolol will alter the bioavailability of propranolol.