Comparison of PCR-based marker systems for the analysis of genetic relationships in cultivated potato

The application of AFLPs, RAPDs and SSRs to examine genetic relationships in the primary northwestern European cultivated potato gene pool was investigated. Sixteen potato cultivars were genotyped using five AFLP primer combinations, 14 RAPD primers, and 17 database-derived SSR primer pairs. All three approaches successfully discriminated between the 16 cultivars using a minimum of one assay. Similarity matrices produced for each marker type on the basis of Nei and Li coefficients showed low correlations when compared with different statistical tests. Dendrograms were produced from these data for each marker system. The usefulness of each system was examined in terms of number of loci revealed (effective multiplex ratio, or EMR) and the amount of polymorphism detected (diversity index, or DI). AFLPs had the highest EMR, and SSRs the highest DI. A single parameter, marker index (MI), which is the product of DI and EMR, was used to evaluate the overall utility of each marker system. The use of these PCR-based marker systems in potato improvement and statutory applications is discussed.Abbreviations: PCR, polymerase chain reaction; AFLP, amplified fragment length polymorphism; RAPD, randomly amplified polymorphic DNA; DNA, deoxyribonucleic acid; EMR, effective multiplex ratio; DI, diversity index; MI, marker index; RFLP, restriction fragment length polymorphism.     

Extragenic Suppressors of Schizosaccharomyces Pombe Rad9 Mutations Uncouple Radioresistance and Hydroxyurea Sensitivity from Cell Cycle Checkpoint Control

Schizosaccharomyces pombe cells that contain a mutation within rad9 are sensitive to ionizing radiation, UV light and hydroxyurea, relative to wild-type strains. In addition, the mutants are moderately hypomutable by UV and unable to delay initiation of mitosis after treatment with radiation or hydroxyurea. Three radioresistant derivatives of rad9::ura4 cells were isolated, and each contained a single unique extragenic suppressor responsible for the acquired resistance. The suppressor loci also conferred radioresistance upon cells containing rad9-192, which differs from rad9(+) by a single base pair change. The suppressors additionally enhanced the radioresistance of cells containing rad3-136, a mutation that leads to phenotypes similar to those mediated by rad9::ura4. None of the derivatives of rad9::ura4 cells recovered the ability to delay cycling in G2 after exposure to ionizing radiation or UV light. All three suppressor derivatives, relative to the parental rad9::ura4 strain, also exhibited a moderate increase in resistance to the DNA replication inhibitor hydroxyurea without gaining the ability to stop progression into mitosis despite the inhibition of DNA synthesis. Results are discussed in terms of models to explain the putative role of rad9 and the suppressor genes in promoting radioresistance and mediating checkpoint controls responsive to DNA damage or incomplete DNA replication.     

Ultrastructural localization of adenosine diphosphatase activity in cultured aortic endothelial cells

Summary Electron microscope cytochemical studies demonstrate that the plasma membrane of cultured aortic endothelial cells contain significant amounts of adenosine diphosphatase. The activity is due to an ectoenzyme on the upper surface of the cell. Intracellular activity was noted in multilamellar bodies.     

Transcriptional and translational control of the biphasic increase in ornithine decarboxylase activity in liver

The requirements for protein and RNA synthesis for each of the two increases in liver ornithine decarboxylase activity after the injection of unoperated rats with a solution containing glucagon and after 70% hepatectomy were studied with cycloheximide and actinomycin D. Protein synthesis is required for both increases whereas RNA formation is essential for the first elevation only. The second increase appears to be dependent upon RNA that is made during the period of the first rise in activity.The two rises in the decarboxylase activity may be caused by different stimuli. After the injection of the mixture with glucagon, the first elevation is accompanied by increases in hepatic tyrosine aminotransferase activity and in the rate of transport into liver cells of the model amino acid, α-aminoisobutyrate. Neither an increase in the aminotransferase activity nor in amino acid uptake occurs, however, during the period of the second elevation in the decarboxylase activity.     

Slow Conduction in Cardiac Muscle: A Biophysical Model

Mechanisms of slow conduction in cardiac muscle are categorized and the most likely identified. Propagating action potentials were obtained experimentally from a synthetically grown strand of cardiac muscle (around 50 μm by 30 mm) and theoretically from a one-dimensional cable model that incorporated varying axial resistance and membrane properties along its length. Action potentials propagated at about 0.3 m/s, but in some synthetic strands there were regions (approximately 100 μm in length) where the velocity decreased to 0.002 m/s. The electrophysiological behavior associated with this slow conduction was similar to that associated with slow conduction in naturally occurring cardiac muscle (notches, Wenckebach phenomena, and block). Theoretically, reasonable changes in specific membrane capacitance, membrane activity, and various changes in geometry were insufficient to account for the observed slow conduction velocities. Conduction velocities as low as 0.009 m/s, however, could be obtained by increasing the resistance (r_i) of connections between the cells in the cable; velocities as low as 0.0005 m/s could be obtained by a further increase in r_i made possible by a reduction in membrane activity by one-fourth, which in itself decreased conduction velocity by only a factor of 1/1.4. As a result of these findings, several of the mechanisms that have been postulated, previously, are shown to be incapable of accounting for delays such as those which occur in the synthetic strand as well as in the atrioventricular (VA) node.