accumulates lysine via two systems, one specific for lysine (LysP) and a second inhibited by arginine or ornithine (LAO). The gene encodes a polypeptide of 489 residues. A topological analysis of the LysP protein was performed using gene fusions. Random in-frame fusions of the gene with the or genes were generated. Site-directed mutagenesis was also used to generate additional fusions at specific locations in the gene. Two methods were used to alleviate the problem of lethal expression of some :: fusions. First, ternary fusions were constructed in which the gene was fused at the 5′ end of the gene and the gene fused at specific sites within the gene. In these plasmids expression was controlled by the promoter. Secondly, an strain with a mutation was used with some fusions to maintain the plasmids at a reduced copy number. From analysis of 30 gene fusions, a topological model of the LysP protein is proposed in which the protein has 12 membrane-spanning regions, with the N- and C-termini in the cytosol.


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