Hearing loss involves both genetic and environmental factors. A mutation (A1555G) in the mtDNA has been associated with aminoglycoside-induced and nonsyndromic sensorineural deafness. The pathological significance of this mutation in Caucasoid families has not been established, and its relationship with antibiotic treatment is not well understood. We studied 70 Spanish families with sensorineural deafness (36 congenital and 34 late onset) for the mtDNA A1555G mutation. The A1555G mutation was found in 19 families with maternally transmitted deafness but not in the other 51 families or in 200 control subjects. In 12 families all the patients with the A1555G mutation who received aminoglycosides became deaf, representing 30.3% of the deaf patients in these families. None of the deaf patients from seven other families received aminoglycosides. Overall, only 17.7% of the patients with deafness and the A1555G mutation had been treated with aminoglycosides. The age at onset of deafness was lower (median age 5 years, range 1-52 years) in those treated with aminoglycosides than in those who did not receive antibiotics (median age 20 years, range 1-65 years) (P < .001). The mtDNA of these families belongs to haplotypes common in Europeans. These data indicate that the A1555G mutation accounts for a large proportion of the Spanish families with late-onset sensorineural deafness, that the A1555G mutation has an age-dependent penetrance for deafness (enhanced by treatment with aminoglycosides), and that mtDNA backgrounds probably do not play a major role in disease expression.

Exposure of the yeast Saccharomyces cerevisiae to alkaline stress resulted in adaptive changes that involved remodeling the gene expression. Recent evidence suggested that the calcium-activated protein phosphatase calcineurin could play a role in alkaline stress signaling. By using an aequorin luminescence reporter, we showed that alkaline stress resulted in a sharp and transient rise in cytoplasmic calcium. This increase was largely abolished by addition of EGTA to the medium or in cells lacking Mid1 or Cch1, components of the high affinity cell membrane calcium channel. Under these circumstances, the alkaline response of different calcineurin-sensitive transcriptional promoters was also blocked. Therefore, exposure to alkali resulted in entry of calcium from the external medium, and this triggered a calcineurin-mediated response. The involvement of calcineurin and Crz1/Tcn1, the transcription factor activated by the phosphatase, in the transcriptional response triggered by alkalinization has been globally assessed by DNA microarray analysis in a time course experiment using calcineurin-deficient (cnb1) and crz1 mutants. We found that exposure to pH 8.0 increased at least 2-fold the mRNA levels of 266 genes. In many cases (60%) the response was rather early (peak after 10 min). The transcriptional response of 27 induced genes (10%) was reduced or fully abolished in cnb1 cells. In general, the response of crz1 mutants was similar to that of calcineurin-deficient cells. By analysis of a systematic deletion library, we found 48 genes whose mutation resulted in increased sensitivity to the calcineurin inhibitor FK506. Twenty of these mutations (42%) also provoked alkaline pH sensitivity. In conclusion, our results demonstrated that calcium signaling and calcineurin activation represented a significant component of the yeast response to environmental alkalinization.Calcium-mediated signaling mechanisms are used by virtually every eukaryotic cell to regulate a wide variety or cellular processes, including gene expression. Transient increases in cytosolic calcium results in activation of diverse enzymes, such as the protein phosphatase calcineurin. Calcineurin is a heterodimer of catalytic subunit and regulatory subunits. In the yeast Saccharomyces cerevisiae, the catalytic subunit is encoded by two genes, CNA1 and CNA2 (1), whereas a single gene, CNB1, encodes the regulatory subunit (2). Cells lacking the catalytic subunits, or the regulatory subunit, are deficient in calcineurin activity.Exposure of yeast cells to a number of signals, such as ␣-factor (3, 4), glucose (5), sphingosine (6), and certain stress conditions (7-9), triggers a rise in cytoplasmic calcium. This increase in calcium can be a consequence of external calcium influx or release from internal stores, such as the vacuole, and results in activation of calcineurin. For instance, hyperosmotic shock has been reported to provoke calcium release from vacuolar stores (8) through Yvc1, a member of the transient receptor potential channel family, and to trig...

The mutations in the quinolone resistance-determining region of the gyrA and gyrB genes from 27 clinical isolates of Escherichia coli with a range of MICs of ciprofloxacin from 0.007 to 128 ,ug/ml and of nalidixic acid from 2 to >2,000 ,ug/ml were determined by DNA sequencing. All 15 isolates with ciprofloxacin MICs of .1 ,ug/ml showed a change in Ser-83 to Leu of GyrA protein, whereas in clinical isolates with a MIC of .8 ,ug/ml (11 strains), a double change in Ser-83 and Asp-87 was found. All isolates with a MIC of nalidixic acid of .128 ,ug/ml showed a mutation at amino acid codon Ser-83. Only 1 of the 27 clinical isolates of E. coli analyzed showed a change in Lys-447 of the B subunit of DNA gyrase. A change in Ser-83 is sufficient to generate a high level of resistance to nalidixic acid, whereas a second mutation at Asp-87 in the A subunit of DNA gyrase may play a complementary role in developing the strain's high levels of ciprofloxacin resistance.New fluoroquinolones are broad-spectrum antibacterial agents which inhibit DNA gyrase activity (26). DNA gyrase contains two subunits of GyrA and two subunits of GyrB (13,19). Gyrase A mediates DNA strand breakage and reunion with the Tyr residue at position 122 forming a transient phosphotyrosine linkage with a broken DNA strand. The mechanisms of quinolone resistance essentially fall into two classes: (i) mutations in gyrA (1,2,5,6,8,17,28,30) or gyrB genes (27, 29) or (ii) reduced levels of quinolone accumulation in the cells (3, 4, 9-12). The mutations in the gyrA gene involved in the resistance are clustered in a region between nucleotides 199 (Ala-67) and 318 (Gln-106), which contains nucleotide 247 (Ser-83), the most frequently changed in spontaneus gyrA mutations. In the gyrB gene, two quinolone resistance-determining sites (amino acids 426 and 447) have been found (27,29). The mutation at amino acid codon Asp-426 confers resistance to nalidixic acid and the new fluoroquinolones, whereas the change of Lys-447 results in resistance to nalidixic acid and increased susceptibility to the fluoroquinolones (29). Recently, Heisig et al. (8) identified mutations in the gyrA gene of Escherichia coli 205096, a highly fluoroquinolone-resistant strain (MIC of ciprofloxacin, 128 ,ug/ml). From 1989 to 1993, the level of resistance to ciprofloxacin in our hospital increased from 0 to 16% in E. coli isolated from urine samples. To further assess the importance of these gyrA and gyrB mutations in the acquisition of high-level quinolone resistance, we examined by DNA sequencing 27 clinical isolates of E. coli with a range of MICs of ciprofloxacin from 0.007 to 128 ,ug/ml and of nalidixic acid from 2 to >2,000 ,ug/ml.The clinical isolates of E. coli were obtained from urine samples from outpatients, who had not previously received quinolones,

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