Reversion studies with exrB in Escherichia coli

exrBderivatives of H/r30 and WP2 are sensitive to ultraviolet radiation (UV), methylmethane sulphonate (MMS) and will not form colonies at 42 °C. Revertants to wild type were selected by plating on either nutrient plates containing MMS or nutrient plates incubated at 42 °C. Revertants selected for MMS resistance were temperature- and UV-resistant, and all revertants selected for temperature resistance were MMS and UV resistant. The frequency with which revertants appeared on MMS plates was about eight times as high as it was at 42 °C, and the variance in frequency of revertants among cultures started with small inocula was higher on selection at 42 °C than on MMS. The spontaneous frequency was estimated to be 10−6to 10−7, sufficiently low to suggest a single mutational event. Among wild-type revertants selected at 42 °C there was a stable and an unstable class.exrB+could be co-transduced withmalB+from stable revertants to anexrBstrain, but could not from unstable revertants. None of the revertants could support the growth of amber or ochre mutants of phage T4, nor were amber and ochre suppressedexrBstrains wild type with regards MMS and temperature resistance. The presence of a polarity suppressor in anexrBstrain did not modify resistance to UV or temperature. Neither UV or MMS was able to induce mutations in anexrBstrain.

Accuracy of recall of histories of oral contraceptive use

Published retrospective studies of the relationship between the use of oral contraceptives and disease have assumed that women are able to recall their oral contraceptive histories with reasonable accuracy. The validity of this assumption has been investigated by comparing oral contraceptive histories obtained from 75 women attending family planning clinics with the information contained in the clinic records. It is concluded that simple measures of oral contraceptive use, such as whether the preparations have ever or never been used, whether they are in current use, and the total duration of use, are likely to be remembered with adequate accuracy.

The synthesis of esters of bilirubin

1-Alkyl-3-p-tolytriazenes were used to synthesize the methyl, ethyl, isopropyl and benzyl esters of bilirubin. Treatment of a chloroform solution of bilirubin with the triazene at room temperature gave high yields of the corresponding esters. These were identified by n.m.r. and mass spectroscopy together with elemental analysis. N.m.r. studies also suggest that bilirubin dimethyl ester is in the lactam rather than the lactim form.

Metal complexes of bilirubin in aprotic solvents

Bilirubin reacts with zinc acetate, cadmium acetate or cobaltous acetate in dry dipolar aprotic solvents to form highly coloured complexes. The complex formed in NN-dimethylformamide can be isolated as a solid with bilirubin:zinc:acetate:NN-dimethylformamide molar proportions of 1:3:2:2. Water will decompose these complexes, with the regeneration of bilirubin.