A gene, hisR, involved in the regulation of levels of histidine biosynthetic enzymes in Salmonella typhimurium, maps between a gene, metE, involved in methionine biosynthesis, and a cluster of genes concerned with isoleucine and valine biosynthesis. Bacteria derepressed for the histidine biosynthetic enzymes form rough-looking colonies on media containing high levels (1-2%) of fermentable carbohydrate. This attribute has facilitated genetic analysis of hisR mutants. Two types of experiment demonstrate that transducing fragments in phage P22 lysates are heterogeneous. First, while hisR1208 exhibits about 0.61% joint transduction with ilvC401 and about 3.1% joint transduction with metE338, the ilvC and metE loci appear to be unlinked (less than 0.01% joint transduction). Secondly, particles effective in transduction of ilvC+ have a slightly higher mean buoyant density than those effective in transduction of metE+. Particles effective in joint transduction of ilvC+ hisR or of hisR metE+ appear to have mean buoyant densities which differ from each other and which are intermediate between the densities of those particles active in transduction of ilvC+ or metE+ singly. These results complement those reported in the accompanying paper by Pearce and Stocker (1965) in suggesting that bacterial chromosome fragments active in transduction of a given marker are not uniform-that is, are not all of the same genetic composition.
|Original language||English (US)|
|Number of pages||11|
|State||Published - Nov 1965|
ASJC Scopus subject areas
- Infectious Diseases