The interface phase and the Schottky barrier for a crystalline dielectric on silicon.

The barrier height for electron exchange at a dielectric-semiconductor interface has long been interpreted in terms of Schottky's theory with modifications from gap states induced in the semiconductor by the bulk termination. Rather, we show with the structure specifics of heteroepitaxy that the electrostatic boundary conditions can be set in a distinct interface phase that acts as a "Coulomb buffer." This Coulomb buffer is tunable and will functionalize the barrier-height concept itself.

Physical structure and inversion charge at a semiconductor interface with a crystalline oxide.

We show that the physical and electrical structure and hence the inversion charge for crystalline oxides on semiconductors can be understood and systematically manipulated at the atomic level. Heterojunction band offset and alignment are adjusted by atomic-level structural and chemical changes, resulting in the demonstration of an electrical interface between a polar oxide and a semiconductor free of interface charge. In a broader sense, we take the metal oxide semiconductor device to a new and prominent position in the solid-state electronics timeline. It can now be extensively developed using an entirely new physical system: the crystalline oxides-on-semiconductors interface.

Optical functions of transparent thin films of SrTiO(3), BaTiO(3), and SiO(x) determined by spectroscopic ellipsometry.

A procedure is presented for accurately determining the thickness, optical functions, and surfaceroughness characteristics of thin-film insulators from two-channel spectroscopic polarization-modulation ellipsometry data. For films with minimal surface roughness, the optical functions can be determined over the entire measured spectrum; for rougher films, the analysis of the spectroscopic ellipsometry data yields meaningful values of the optical functions only in the transparent region. In general, the films must be transparent in a given range of wavelengths sampled by the ellipsometer so that at least two interference oscillations can be observed. The use of the procedure is illustrated with the determination of the optical functions of SrTiO(3) and BaTiO(3) thin films grown on MgO, and of SiO(x) films grown on Si. For SrTiO(3) and BaTiO(3), the thin-film results are compared with the measured optical functions of the respective bulk materials.

PCR products generated from unpurified Salmonella DNA are degraded by thermostable nuclease activity.

Oligonucleotide primers designed from repetitive extragenic palindromic (REP) sequences were used to PCR-amplify Salmonella DNA. Unpurified template DNA, present in crude cell extracts, yielded an essentially identical banding pattern to that arising from the use of purified DNA. However, the PCR product derived from the crude preparations did not survive storage at 4 degrees C. This post-PCR DNA degradation, attributed to endogenous Salmonella nucleases, was inhibited by the addition of EDTA, or storage at -20 degrees C.

Genomic subtractive hybridization to isolate species-specific DNA sequences in insects.

Selective enrichment has been used in a number of instances for the isolation of species-specific sequences in prokaryotes. This paper reports the successful application of the technique to insects. Genomic probes were derived to the target species D. funebris and D. simulans. The method involves the biotinylation of non-target 'driver' DNA prepared from the closely related species D. melanogaster and its hybridization to homologous sequences in the target DNA. Hybrid molecules were removed from the reaction by incubation with streptavidin followed by phenol extraction, leaving a preparation enriched for target fragments. All DNA fragments isolated in the D. funebris experiments proved to be specific to that species. Five out of twenty-four fragments screened in the D. simulans experiments were specific when screened with homologous DNA and genomic DNA from its sibling species, D. melanogaster.

Rapid identification of Saccharomyces cerevisiae, Zygosaccharomyces bailii and Zygosaccharomyces rouxii.

Most strains of Saccharomyces cerevisiae, Zygosaccharomyces bailii and Zygosaccharomyces rouxii have been found to contain plasmid DNA. The sequences of the plasmids from these three yeasts are known to be different. We have used two primers within the plasmid from each yeast species in a multiplex polymerase chain reaction (PCR) to discriminate between these three yeasts. The primers were designed to give easily distinguishable fragment sizes when run on a simple agarose gel. Due to the sensitivity of PCR, crude cells can be used with no need to isolate DNA. The method is rapid when compared with current methods.

A microtiter plate-based assay for phosphoenolpyruvate carboxylase.

A sensitive, quantitative assay for phosphenolpyruvate carboxylase which utilizes microtiter plates is described. The assay depends upon the production of a colored compound in the reaction between oxaloacetate, the product of the phosphoenolpyruvate reaction, and the dye Fast Violet B. The method is particularly appropriate for monitoring chromatographic eluates and its utility for this purpose is demonstrated by the detection of phosphoenolpyruvate carboxylase in fractions of crude maize extract separated by size-exclusion chromatography.

Molecular analysis of actinidin, the cysteine proteinase of Actinidia chinensis.

We have isolated and sequenced two very similar cDNA clones of 1145 and 809 bp length, from a fruit-specific library of Actinidia chinensis, the larger encoding all 220 amino acids of actinidin, showing 91% homology to the published amino acid sequence. Both cDNAs code for an additional 25 amino acids following the mature carboxy terminus of actinidin. The larger clone has coding potential for 57 residues of an amino-terminal extension with considerable homology to amino-terminal sequences of other cysteine proteinases. From size determination of both mRNA (1.4 kb) and immunoprecipitated in vitro translation product (39 kDa) it was estimated that actinidin is synthesised as a precursor approximately 15 kDa larger than the mature protein. Both proteolytic cleavage sites are located on the surface of the molecule as illustrated by the hydropathy profile of the deduced amino acid sequence. Features of the prosegment primary sequence are considered with regard to a possible mechanism of inactivation of the proteinase, by analogy with other proteolytic zymogens. The presence of three potential glycosylation sites, one within the carboxy-terminal and two in the amino-terminal extension, are consistent with subcellular location of the enzyme within membrane-bound organelles. Results from a Southern blot suggest that actinidin is encoded by a multigene family of up to ten members. Actinidin gene expression, both at the level of mRNA and protein, is largely restricted to the fruit of the plant, where the level of actinidin mRNA accumulates early during development.

Molecular cloning of two cysteine proteinases from paw-paw (Carica papaya).

Two cDNA clones for plant cysteine proteinases have been isolated from a Carica papaya (paw-paw, papaya) leaf tissue cDNA library by using a mixture of 16 synthetic oligodeoxyribonucleotides as a hybridization probe. The inserted regions are 311 and 440 base-pairs in length and have the potential to encode a region corresponding to the C-terminal region of two proteins which are homologous with the known plant cysteine proteinases and the mammalian thiol cathepsins. One of the sequences shows a high (greater than 77%) homology with the plant cysteine proteinase papain, the other is closely related to papaya chymopapain. One sequence contains all, and the other most, of the 3' untranslated region of the mRNA. The inserts were used as specific probes in Northern Blot analyses giving an estimated size for the two mRNA species of 1.45 kilobases.

Deletion analysis of essential genes of Escherichia coli: investigation of the btuB-rpoBC interval.

A method is described for deletion mapping of essential genes in Escherichia coli. It involves the isolation of secondary-site insertions of lambda cI857plac5 into an F' plasmid. The transposed lacZ gene is useful both for the ready screening of plasmid-phage cointegrates and for rapid analysis of deletions that extend from the site of phage integration into the bacterial genes carried on the substituted plasmid. Such deletions may be used to 'hook-up' bacterial cistrons to the powerful lac promoter. We report the application of this technique to the study of the btuB-rpoBC interval, a cluster of genes encoding components of the transcription-translation apparatus.