Biomedical subjects

J S Kornher

Publications and source records attributed to J S Kornher.

3 recordsLinked to original sources

PubMed1989

Mutation detection using nucleotide analogs that alter electrophoretic mobility.

A simple primer extension assay has been developed to distinguish homologous DNA segments differing by as little as a single nucleotide. DNA strands are synthesized with one of the four natural nucleotides replaced with an analog that affects electrophoretic mobility. DNAs that are the same length but differ in the number of analog molecules per strand exhibit different mobilities on a sequencing gel. In combination with the polymerase chain reaction (PCR; 1, 2), this method has been used to distinguish mutant and normal alleles of the human insulin receptor gene that differ by a single-base substitution. The method appears to be generally applicable to the detection of any nucleotide polymorphism in any segment of DNA.

Base Sequence↗

PubMed1986

Proximity-dependent enhancement of Sgs-4 gene expression in D. melanogaster.

A weakly expressed allele of Sgs-4 obtained from the Kochi strain of D. melanogaster (Sgs-4K) increases 4-fold in levels of accumulated transcript when paired with a wild-type (Oregon-R) Sgs-4 allele (Sgs-4ORE) and increases 9-fold when paired with a duplication of the wild-type Sgs-4 allele Confluens (Sgs-4Co). There is no enhancement of expression when Sgs-4K is paired with the Sgs-4 null allele Ber-I (Sgs-4BER) or with another weakly expressed Sgs-4 allele, Hikone-R (Sgs-4HIK); there is minimal enhancement when chromosome pairing is disrupted near the Sgs-4 locus by rearrangement of the wild-type Sgs-4 allele. Cytological analysis of third instar salivary gland nuclei from Kochi/Confluens heterozygotes suggests that complete pairing is not essential for Sgs-4K enhancement. Interactions between homologous loci that could produce a trans enhancement effect are discussed and a hypothesis is formulated to test the significance of specific upstream sequences from both alleles in expression enhancement.

Alleles↗

PubMed1986

Variegated expression of the Sgs-4 locus in Drosophila melanogaster.

Experiments on T(1;4)wm258-21 larvae of Drosophila melanogaster are described which establish the existence of a salivary gland specific marker for position-effect variegation. The marker is a glue protein gene called Sgs-4 which is expressed during the third larval instar. Using temperature as a variegation modifier, we showed that cytological compaction for the Sgs-4 chromosomal locus is enhanced at 17 degrees C and reduced at 29 degrees C. We also found that the Sgs-4 protein and transcript from salivary glands at 17 degrees C accumulate to roughly half the levels found in salivary glands at 29 degrees C. Southern analysis suggested that the Sgs-4 locus at 17 degrees C is polytenized to roughly one-third the level at 29 degrees C. The results are discussed with respect to alternative models of variegation.

DNA↗