Biomedical subjects

S Kieffer-Higgins

Publications and source records attributed to S Kieffer-Higgins.

2 recordsLinked to original sources

PubMed1993

Characterization of the cobalamin (vitamin B12) biosynthetic genes of Salmonella typhimurium.

Salmonella typhimurium synthesizes cobalamin (vitamin B12) de novo under anaerobic conditions. Of the 30 cobalamin synthetic genes, 25 are clustered in one operon, cob, and are arranged in three groups, each group encoding enzymes for a biochemically distinct portion of the biosynthetic pathway. We have determined the DNA sequence for the promoter region and the proximal 17.1 kb of the cob operon. This sequence includes 20 translationally coupled genes that encode the enzymes involved in parts I and III of the cobalamin biosynthetic pathway. A comparison of these genes with the cobalamin synthetic genes from Pseudomonas denitrificans allows assignment of likely functions to 12 of the 20 sequenced Salmonella genes. Three additional Salmonella genes encode proteins likely to be involved in the transport of cobalt, a component of vitamin B12. However, not all Salmonella and Pseudomonas cobalamin synthetic genes have apparent homologs in the other species. These differences suggest that the cobalamin biosynthetic pathways differ between the two organisms. The evolution of these genes and their chromosomal positions is discussed.

Amino Acid Sequence↗

PubMed1988

Multiplex DNA sequencing.

The increasing demand for DNA sequences can be met by replacement of each DNA sample in a device with a mixture of N samples so that the normal throughput is increased by a factor of N. Such a method is described. In order to separate the sequence information at the end of the processing, the DNA molecules of interest are ligated to a set of oligonucleotide "tags" at the beginning. The tagged DNA molecules are pooled, amplified, and chemically fragmented in 96-well plates. The resulting reaction products are fractionated by size on sequencing gels and transferred to nylon membranes. These membranes are then probed as many times as there are types of tags in the original pools, producing, in each cycle of probing, autoradiographs similar to those from standard DNA sequencing methods. Thus, each reaction and gel yields a quantity of data equivalent to that obtained from conventional reactions and gels multiplied by the number of probes used. To date, even after 50 successive probings, the original signal strength and the image quality are retained, an indication that the upper limit for the number of reprobings may be considerably higher.

Automation↗