Translational Regulation of Genes in Salmonella typhimurium by Vitamin B12 BY SOLVEIG RAVNUM

Ravnum, S. 2000. Translational regulation of genes in Salmonella typhimurium by vitamin B12 Acta Universitatis Upsaliensis. Comprehensive Summaries of Uppsala Dissertations from the faculty of Science and Technology. 591. 52pp. Uppsala. ISBN 91-554-4874-7. In this thesis I have studied the mechanism by which vitamin B12 regulates the expression of the cob operon and the btuB gene in Salmonella typhimurium. The cob operon encodes most of the 25 genes required for the de novo synthesis of vitamin B12, and the btuB gene encodes the outer membrane protein needed for transport of exogenous vitamin B12 into the cell. Vitamin B12 is used as a cofactor in four enzymatic reactions in Salmonella typhimurium. The regulation by vitamin B12 of the cob operon and the btuB gene requires sequences in the long leader regions of the respective mRNAs. Proper folding of the leader mRNA is essential for normal repression, in particular a hairpin structure that sequesters the ribosomal binding site (RBS). The upstream leader region contains two conserved sequence elements that are required for the vitamin B12 regulation; the translational enhancer (TE) element element and the B12 box. The TE element confers its enhancer function by resolving the downstream inhibitory RBS hairpin through basepairing with nucleotides in the stem. In the presence of vitamin B12, either B12 itself, or a B12 regulatory factor binds to the upstream leader region and prevents the enhancer function. This will inhibit unfolding of the RBS hairpin and repress translation. Solveig Ravnum, Department of Cell and Molecular Biology, Biomedical Center, Box 596, SE-751 24 Uppsala, Sweden © Solveig Ravnum 2000