Thialysine-Resistant Mutant of SALMONELLA TYPHIMURIUM with a Lesion in the thrA Gene
AUTOR(ES)
Jegede, Victor A.
RESUMO
A mutant of Salmonella typhimurium was selected for its spontaneous resistance to the lysine analog, thialysine (S-2-aminoethyl cysteine). This strain, JB585, exhibits a number of pleiotropic properties including a partial growth requirement for threonine, resistance to thiaisoleucine and azaleucine, excretion of lysine and valine, and inhibition of growth by methionine. Genetic studies show that these properties are caused by a single mutation in the thrA gene which encodes the threonine-controlled aspartokinase-homoserine dehydrogenase activities. Enzyme assays demonstrated that the aspartokinase activity is unstable and the threonine-controlled homoserine dehydrogenase activity absent in extracts prepared from the mutant. These results explain the growth inhibition by methionine because the remaining homoserine dehydrogenase isoenzyme would be repressed by methionine, causing a limitation for threonine. The partial growth requirement for threonine during growth in glucose minimal medium may also, by producing an isoleucine limitation, cause derepression of the isoleucine-valine enzymes and provide an explanation for both the valine excretion, and azaleucine and thiaisoleucine resistance. The overproduction of lysine may confer the thialysine resistance.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1213538Documentos Relacionados
- Nucleotide sequence of the thrA gene of Escherichia coli.
- Genetic Analysis of thr Mutations in Salmonella typhimurium
- Defective Guanine Uptake in an 8-Azaguanine-resistant Mutant of Salmonella typhimurium
- Genetic mapping of mutations in a highly radiation-resistant mutant of Salmonella typhimurium LT2.
- Host response to infection with a temperature-sensitive mutant of Salmonella typhimurium in a susceptible and a resistant strain of mice.
