Subject index vol. 70 (1980)

Antibiotic-resistant (either to erythromycin or chloramphenicol) temperature-sensitive mutants were isolated with about the same frequency in 2 strains of the petite negative yeast K. lactis.The ery^R and cap^R mutants isolated in the strain K. lactis CBS 2359 showed with high frequency both a lethal-conditioned (lc) or a petite temperature-sensitive (pts) phenotype, whereas amongst the many ery^R and cap^R mutants isolated in the strain K. lactis CBS 2360 only lc phenotypes appeared. In the mutants isolated from K. lactis CBS 2360, one growth cycle in the presence of ethidium bromide irreversibly blocked the transmission of antibiotic resistance and temperature sensitivity (lc and pts), whereas at least 2 growth cycles were required to give the same results for the mutants isolated in K. lactis CBS 2359.The spontaneous reversion frequencies for the temperature sensitivity were about the same for the lc mutants isolated in the 2 strains, but the frequencies of co-reversion of the antibiotic resistance were higher in ery^Rlc and cap^Rlc mutants isolated from K. lactis CBS 2360.The analysis of the effect of the exposure to erythromycin or to the temperature of 36°C on protein synthesis carried out by isolated mitochondria of 2 ery^Rlc mutants of K. lactis CBS 2360 and CBS 2359 showed that, in these mutants, mitochondrial protein synthesis became resistant to the drug and sensitive to temperature. The exposure at 36°C, before protein synthesis was inactived, determined in these mutants a condition of sensitivity to the antibiotic, suggesting that even though the 2 K. lactis strains differ in some aspects concerning the behaviour of their mitochondrial information they might depend, as to their petite-negative character, on the role that mitochondrial protein synthesis has in cell division.