Cs؉ was found to induce expression of the kdpFABC operon, encoding a high-affinity K ؉ uptake system of Escherichia coli. Quantitative expression analyses at the transcriptional and translational levels reveal that CsCl causes much higher induction of kdpFABC than does NaCl. A decrease of the intracellular K ؉ concentration is found in cells exposed to CsCl. The results indicate that kdpFABC expression is induced when the intracellular K ؉ concentration is lowered. Moreover, the results imply that the signal transduction cascade mediated by KdpD and KdpE is able to integrate multiple signals.

No abstract

Between the genes for tRNA(gin) and tRNA(ile) an open reading frame of 227 amino acids has been identified which is unique among known mitochondrial genomes and which has been termed urf a (Lang et al. 1983; Kornrumpf et al. 1984). It uses the "mitochondrial" genetic code, i.e., it contains a TGA codon, whereas all other protein-encoding genes, and all but one intronic open reading frame, use the "standard" genetic code (UGG for tryptophan). A previous paper has demonstrated that "mutator" strains show an increased formation of mitochondrial drug-resistant and respiration-deficient mutants (including deletions). In this paper we show that the mutator activity is correlated with mutations in urf a. A detailed analysis of one urf a mutant is presented (anar-6), where the deletion of an A residue leads to a frameshift mutation and consequently to premature termination of the putative protein. The phenotype of colonies originating from a single mutant clone varies from no growth up to full growth on non-fermentable substrate. This phenomenon of phenotypic segregation can be explained by the ability of the cell to perform translational frameshifting. A detailed analysis of the DNA sequence and the putative urf a protein will be presented and a possible function of the protein will be discussed.

No abstract