Optimizing purebred selection for crossbred performance using QTL with different degrees of dominance

A method was developed to optimize simultaneous selection for a quantitative trait with a known QTL within a male and a female line to maximize crossbred performance from a two-way cross. Strategies to maximize cumulative discounted response in crossbred performance over ten generations were derived by optimizing weights in an index of a QTL and phenotype. Strategies were compared to selection on purebred phenotype. Extra responses were limited for QTL with additive and partial dominance effects, but substantial for QTL with over-dominance, for which optimal QTL selection resulted in differential selection in male and female lines to increase the frequency of heterozygotes and polygenic responses. For over-dominant QTL, maximization of crossbred performance one generation at a time resulted in similar responses as optimization across all generations and simultaneous optimal selection in a male and female line resulted in greater response than optimal selection within a single line without crossbreeding. Results show that strategic use of information on over-dominant QTL can enhance crossbred performance without crossbred testing.     

Efficient ethanol production from glucose, lactose, and xylose by recombinant Escherichia coli

Lactose and all of the major sugars (glucose, xylose, arabinose, galactose, and mannose) present in cellulose and hemicellulose were converted to ethanol by recombinant Escherichia coli containing plasmid-borne genes encoding the enzymes for the ethanol pathway from Zymomonas mobilis. Environmental tolerances, plasmid stability, expression of Z. mobilis pyruvate decarboxylase, substrate range, and ethanol production (from glucose, lactose, and xylose) were compared among eight American Type Culture Collection strains. E. coli ATCC 9637(pLO1297), ATCC 11303(pLO1297), and ATCC 15224(pLO1297) were selected for further development on the basis of environmental hardiness and ethanol production. Volumetric ethanol productivities per hour in batch culture were 1.4 g/liter for glucose (12%), 1.3 g/liter for lactose (12%), and 0.64 g/liter for xylose (8%). Ethanol productivities per hour ranged from 2.1 g/g of cell dry weight with 12% glucose to 1.3 g/g of cell dry weight with 8% xylose. The ethanol yield per gram of xylose was higher for recombinant E. coli than commonly reported for Saccharomyces cerevisiae with glucose. Glucose (12%), lactose (12%), and xylose (8%) were converted to (by volume) 7.2% ethanol, 6.5% ethanol, and 5.2% ethanol, respectively.     

Identification of a novel casein kinase activity in HeLa cell nuclei

Three casein kinase activities have been resolved by column chromatography of HeLa cell nuclear extracts. In addition to casein kinases NI and NII, which have been described in other cell types, HeLa nuclei contain a third casein kinase activity which we have named NIII. NIII is a cyclic nucleotide-independent casein kinase which uses either Mg2+ or Mn2+ as a divalent cation, but is inhibited by increasing NaCl concentrations in the presence of Mg2+ and has optimal activity at 50 mM NaCl in the presence of Mn2+. In Mg2+, NIII uses only ATP as a phosphate donor, but in Mn2+ NIII transfers phosphate from either ATP or GTP. NIII phosphorylates the serine and threonine residues of casein, but does not phosphorylate phosvitin or calf thymus histones.     

Effect of postnatal development on calcium currents and slow charge movement in mammalian skeletal muscle

Single- (whole-cell patch) and two-electrode voltage-clamp techniques were used to measure transient (Ifast) and sustained (Islow) calcium currents, linear capacitance, and slow, voltage-dependent charge movements in freshly dissociated fibers of the flexor digitorum brevis (FDB) muscle of rats of various postnatal ages. Peak Ifast was largest in FDB fibers of neonatal (1-5 d) rats, having a magnitude in 10 mM external Ca of 1.4 +/- 0.9 pA/pF (mean +/- SD; current normalized by linear fiber capacitance). Peak Ifast was smaller in FDB fibers of older animals, and by approximately 3 wk postnatal, it was so small as to be unmeasurable. By contrast, the magnitudes of Islow and charge movement increased substantially during postnatal development. Peak Islow was 3.6 +/- 2.5 pA/pF in FDB fibers of 1-5-d rats and increased to 16.4 +/- 6.5 pA/pF in 45-50-d-old rats; for these same two age groups, Qmax, the total mobile charge measurable as charge movement, was 6.0 +/- 1.7 and 23.8 +/- 4.0 nC/microF, respectively. As both Islow and charge movement are thought to arise in the transverse-tubular system, linear capacitance normalized by the area of fiber surface was determined as an indirect measure of the membrane area of the t-system relative to that of the fiber surface. This parameter increased from 1.5 +/- 0.2 microF/cm2 in 2-d fibers to 2.9 +/- 0.4 microF/cm2 in 44-d fibers. The increases in peak Islow, Qmax, and normalized linear capacitance all had similar time courses. Although the function of Islow is unknown, the substantial postnatal increase in its magnitude suggests that it plays an important role in the physiology of skeletal muscle.     

Expression of Different Levels of Ethanologenic Enzymes from Zymomonas mobilis in Recombinant Strains of Escherichia coli

The expression of Zymomonas mobilis genes encoding pyruvate decarboxylase and alcohol dehydrogenase II in Escherichia coli converted this organism from the production of organic acids to the production of ethanol. Ethanol was produced during both anaerobic and aerobic growth. The extent to which these ethanologenic enzymes were expressed correlated with the extent of ethanol production. The replacement of organic acids with ethanol as a metabolic product during aerobic and anaerobic growth resulted in dramatic increases in final cell density, indicating that these acids (and the associated decline in pH) are more damaging than the production of ethanol. Of the plasmids examined, the best plasmid for growth and ethanol production expressed pyruvate decarboxylase and alcohol dehydrogenase II at levels of 6.5 and 2.5 IU/mg of total cell protein, respectively.     

Determination of the intracellular concentration of ethanol in Saccharomyces cerevisiae during fermentation.

Considerable controversy exists concerning the intracellular concentration of ethanol in Saccharomyces cerevisiae during fermentation. This controversy results from problems in the measurement of the intracellular concentration of compounds like ethanol, which are being produced rapidly by metabolism and potentially diffuse rapidly from the cell. We used a new method for the determination of intracellular ethanol based on the exclusion of [14C]sorbitol to estimate the aqueous cell volume. This method avoided many of the technical problems in previous reports. Our results indicate that the extracellular concentrations of ethanol in fermenting suspensions of S. cerevisiae are less than or equal to those in the intracellular environment and do not increase to the high levels previously reported even during the most active stages of batch fermentation.     

Airway dynamics in transition between peak and maximal expiratory flow

Expiratory flow-volume curves with periodic interruption of flow showed flow transients exceeding maximal flow (Vmax) measured on the maximum expiratory flow-volume (MEFV) curve in a mechanical lung model and in five tracheotomized, vagotomized, open-chest, anesthetized dogs. Direct measurement of flow from the collapsing model airway showed that the volume of the flow transients in excess of the MEFV envelope was greater than that from the collapsing airway. Determination of wave-speed flows from local airway transmural pressure-area curves (J. Appl. Physiol. 52: 357-369, 1982) and photography of the airway led to the following conclusions. Flow transients exceeding Vmax are wave-speed flows determined by an initial and unstable configuration of the flow-limiting segment (FLS) with maximum compression in the midportion. The drop in flow from the peak to the following plateau is due to development of a more stable airway configuration with maximum compression at the mouthward end with a smaller area and a smaller maximal flow. When FLS jumps to a more peripheral position, the more distal airways may pass through similar configurational changes that are responsible for the sudden decrease of flow (the "knee") seen on most MEFV curves from dogs.