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Biomedical subjects

J A Welsch

Publications and source records attributed to J A Welsch.

7 recordsLinked to original sources
PubMed1995

Cellular and molecular events in a newly organizing lateral root meristem.

Spontaneous or auxin-induced lateral root formation in radish and Arabidopis provides an efficient system in which to examine molecular and cellular events associated with the initiation of a new meristem. Subtracted cDNA libraries made at different times in lateral root initiation were used as a source of genes that are expressed differentially during this developmental process, and expression studies on a small gene family of ribosomal protein genes were conducted. From analysis of cell division patterns in pericycle cells the number of founder cells for lateral roots was established. By the use of in vitro growth assays lateral root formation was determined to be a two-stage process. First a primordium is formed, and subsequently a subset of primordial cells begins to function as the lateral root apical meristem. This mode of root development has implications for pattern formation in newly organizing organs.

Arabidopsis↗
PubMed1994

The Arabidopsis phytochrome A gene has multiple transcription start sites and a promoter sequence motif homologous to the repressor element of monocot phytochrome A genes.

We have determined the sequence of the phytochrome A gene (PHYA) and its flanking DNA from Arabidopsis thaliana and have identified transcription start sites for three nested transcripts of increasing length. The overall structure of the gene is similar as regards exon/intron organization to other angiosperm PHY genes characterized. The triple transcription start site arrangement is similar to that of pea PHYA but different from the single start site of oat, rice and maize PHYA genes, indicating a possible monocot-dicot difference. Comparison of the Arabidopsis PHYA promoter sequence with others available indicates that both pea and Arabidopsis promoters contain a DNA element with a core sequence motif identical to one conserved in all existing monocot PHYA sequences and defined by functional assay in the oat PHYA gene as repressor element, RE1, responsible for negative light regulation.

Amino Acid Sequence↗
PubMed1989

Transformation of Neurospora crassa by an integrative transforming plasmid is not enhanced by ribosomal DNA sequences.

Two integrative transforming plasmids of Neurospora crassa that differed only by the presence of almost all of a ribosomal DNA repeat unit on one plasmid were constructed. The plasmids were used to test the target concentration hypothesis which states that the transformation frequency is proportional to the number of genomic copies of a homologous sequence located on the transforming plasmid. Since there are approx. 200 copies of the rDNA sequences in the genome, the target concentration hypothesis would have been proved if the transformation frequency was 200-fold higher for the rDNA-containing plasmid compared with the plasmid without rDNA. The results indicated no difference in the transformation for the two plasmids, thereby providing no support for the hypothesis. The target concentration hypothesis has been proved for yeast, and thus mechanisms different from that responsible for integrative transformation in yeast must operate in N. crassa, perhaps including non-homologous recombination events.

DNA, Fungal↗
PubMed1987

Methods for DNA extraction from Candida albicans.

Three different methods are described for the extraction of total genomic DNA from the dimorphic fungus Candida albicans. One method, which enables a large number of cultures to be processed simultaneously, involves pulverizing dried cells with glass beads and then allowing the disrupted cells to break apart, autolyse, by incubation in a solution which includes sorbitol and a nonionic detergent. DNA extraction by a second method with a French pressure cell can be utilized on cultures in any phase of growth, but is not practical for processing numerous samples. The third method, which involves induction of spheroplasts, is commonly used for DNA extraction from various yeasts but is not suited for processing many samples simultaneously. The DNA extracted with the three procedures is comparable in quality; in particular, it is of high molecular size (greater than 30 kbp) and reacts readily with DNA-modifying enzymes such as restriction endonucleases.

Candida albicans↗
PubMed1987

Different levels of DNA methylation in yeast and mycelial forms of Candida albicans.

Isotope dilution gas chromatography-mass spectrometry analysis of genomic DNAs isolated from three Candida albicans isolates showed significant differences in the amounts of 5-methyldeoxycytidine (m5Cyt) in DNA from yeast-form and from mycelial-form cells; the moles percent m5Cyt were 0.11, 0.11, and 0.097 for yeast-form DNA and 0.045, 0.053, and 0.047 for mycelial-form DNA for the three isolates Sh8, 9938, and B311, respectively. The lower m5Cyt values for mycelial-form cells suggest that those cells may exhibit significantly greater gene activity than yeast-form cells.

Candida albicans↗