Understanding biochemistry: structure and function of nucleic acids.

Nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), carry genetic information which is read in cells to make the RNA and proteins by which living things function. The well-known structure of the DNA double helix allows this information to be copied and passed on to the next generation. In this article we summarise the structure and function of nucleic acids.

A new chromosomal locus associated with gut-modulated phenotypes in Salmonella enterica serotype typhimurium.

A cosmid DNA library had been constructed previously from 40-kb fragments of genomic DNA from a virulent invasive strain of Salmonella enterica serotype Typhimurium (TML) in an avirulent hypo-invasive Typhimurium strain (LT7). Selection of invasive clones from the library was attempted by iterative passage through a rabbit ileal organ culture. After the fourth passage, a clone, designated LT7(pHC20-2), was isolated.

Invasiveness of Salmonella serotypes Typhimurium and Enteritidis of human gastro-enteritic origin for rabbit ileum: role of LPS, plasmids and host factors.

An organ culture system involving explants of distal rabbit ileum was used to study the roles of lipopolysaccharide (LPS) and plasmids in primary invasiveness for enterocytes in situ of strains of Salmonella serotypes Typhimurium and Enteritidis. Long-chain LPS per se does not confer invasiveness on Typhimurium, as known avirulent, hypo-invasive strains express smooth LPS. However, the invasiveness of a naturally occurring rough isogenic derivative of Salmonella serotype Enteritidis PT 4 was about half that of its wild-type parent.

A histotoxin produced by Salmonella.

Salmonella Typhimurium strain GM3, known to be histotoxic for explants of terminal rabbit ileum in vitro, produces similar lesions in vitro when sterile filtrates, obtained from live organisms after interaction with gut explants in vitro, are used and when rabbit ligated ileal loops are challenged with live organisms. Epithelial damage occurs rapidly, within 2 h of adding organisms or sterile filtrates. This evidence is construed in terms of a secreted salmonella histotoxin that causes epithelial damage, detaching enterocytes which rapidly degenerate into spheroid cells devoid of microvilli.