Rapid, high fidelity analysis of simple sequence repeats on an electronically active DNA microchip.

We describe a method for the discrimination of short tandem repeat (STR) alleles based on active microarray hybridization. An essential factor in this method is electronic hybridization of the target DNA, at high stringency, in <5 min. High stringency is critical to avoid slippage of hybrids along repeat tracts at allele-specific test sites in the array. These conditions are attainable only with hybridization kinetics realized by electronic concentration of DNA. A sandwich hybrid is assembled, in which proper base stacking of juxtaposed terminal nucleotides results in a thermodynamically favored complex. The increased stability of this complex relative to non-stacked termini and/or base pair mismatches is used to determine the identification of STR alleles. This method is capable of simultaneous and precise identification of alleles containing different numbers of repeats, as well as mutations within these repeats. Given the throughput capabilities of microarrays our system has the potential to enhance the use of microsatellites in forensic criminology, diagnostics and genetic mapping.

Increased migration rate observed in DNA from evidentiary material precludes the use of sample mixing to resolve forensic cases of identity.

The analysis of restriction fragment length polymorphisms in forensic DNA samples can be used to determine whether any two or more samples have the same biological origin. However, sometimes DNA recovered from evidentiary material, such as blood or semen stains, migrates at a different rate than an exemplar sample. This difference in migration, while maintaining the same overall pattern, produces a shift in the position of the bands. To verify that a shift in migration has occurred between evidence and exemplar samples, we have utilized two DNA probes that recognize DNA fragments that do not vary in size between individuals (monomorphic). The results obtained with this type of internal control show that differences in migration rate between exemplar and evidentiary samples can be recognized and accounted for and do not affect the ability to decide whether two patterns match. A common practice in many analytical tests, to show identity between two samples, is to test the properties of the samples individually and mixed. However, this approach is not applicable to all forensic DNA identity tests. In many cases, DNA from forensic samples may be irreversibly modified and this can alter the migration rate of the DNA samples. Thus, in a mixture of DNA from exemplar and evidence, the same polymorphic DNA fragments may not comigrate and produce a composite pattern which could lead to false exclusions.

Anaerobiosis induces transcription but not translation of sucrose synthase in maize.

This report examines the effect of anaerobic stress on the expression of sucrose synthase in maize (Zea mays L.). Following 24 hours of anaerobic treatment, alcohol dehydrogenase displayed the classical characteristics of induction: increased mRNA and protein levels. However, there was no detectable increase in sucrose synthase specific proteins by either native or denaturing Western blot analysis nor was there an increase in sucrose synthase activity. Anaerobic treatment did induce significantly higher steady state levels of sucrose synthase mRNA. Even though previous work has implicated sucrose synthase as an anaerobically induced protein, the data in this report suggest that sucrose synthase is not inducible at the protein level by anaerobic treatment.

The effect of temperature on biochemical and molecular properties of Drosophila alcohol dehydrogenase.

The gene products of the two major alleles of alcohol dehydrogenase (ADH-F and ADH-S) have been subjected to kinetic and biochemical analyses over a range of temperatures. Although temperature was found to have a significant effect on both kinetic and biochemical properties of Drosophila ADH, no significant differential effect was observed between the major ADH allozymes. The results are discussed within the context of the selective maintenance of Adh polymorphism in natural populations.

The effect of alcohol stress on nicotinamide adenine dinucleotide (NAD+) levels in Drosophila.

Previous studies carried out in mammalian systems indicated that an organism's NAD+/NADH balance is carefully regulated but can be destabilized by dietary stresses. Since Drosophila alcohol dehydrogenase (ADH) uses NAD+ to remove a hydrogen from ethanol in the first step of alcohol catabolism, it is possible that under alcohol stress conditions the in vivo NAD+ levels in Drosophila may decrease. In this study genetically homozygous flies were stressed with maximally sublethal concentrations of ethanol (10%) for periods of up to 24 hr. The results indicate that NAD+ levels do in fact drop by at least 20% in response to ethanol stress. Evidence is presented that suggests that this decrease is the direct result of ADH-mediated catabolism.