SUMMARY: Certain point and deletion mutants with lesions in the cysJ gene of Salmonella typhimurium have low levels of enzymes coded by the cysI and cysH genes. These results support the hypothesis that an operon exists comprising genes cysJ, I and H which is transcribed in the direction from cysJ to H. The nearby cysC and cysD genes do not form part of this cysJIH operon.
SUMMARY: In a sample of 52 wild-type isolates of Aspergillus nidulans, penicillin titre ranged from 0.0 to 14.4 units/ml. These differences in titre were under genetic control. Most of the variation between isolates was attributable to differences between heterokaryon-compatibility groups although significant differences were also found within groups. Genetic variation for penicillin titre was observed among the progeny in four of seven crosses between wild-type isolates. In these four crosses the variation was continuous, indicating that this is a polygenically determined character, and progeny with titres superior and inferior to those of the parents were produced. The genes determining penicillin production are predominantly additive in their action. Crosses between heterokaryon-incompatible isolates generated more genetic variation than those involving compatible parents, supporting the hypothesis that heterokaryon-compatible isolates are frequently closely related.
SUMMARY: A total of 41 mutants lacking NADP L-glutamate dehydrogenase (NADP-GDH) activity have been studied. All the mutations were located at the gdhA locus within 0.1% recombination of gdhA1. Two mutants, gdhA1 and gdhA2, out of five examined, produced cross-reacting material which neutralized NADP-GDH antiserum. The mutant gdhA9 has altered Km values for all five substrates: ammonium, α-ketoglutarate, L-glutamate, NADPH and NADP. The mutant gdhA20 had temperature-sensitive growth, abnormal ammonium-regulation characteristics and thermolabile NADP-GDH activity. These results show that gdhA is the structural gene for NADP-GDH.
SUMMARY: Nucleic acid preparations from Agrobacterium tumefaciens (Smith & Townsend) Conn., have been tested for tumorigenic activity on a number of bioassay systems including carrot root explants, sunflower and tobacco stem segments, callus cultures of sunflower, tobacco and carrot, and sunflower stems. The methods used to isolate and test the DNA included those which have been reported to be successful for the induction of tumours. Strict precautions were taken to ensure that the DNA samples used in the tests were free of viable bacterial cells. In the large number of tests carried out under various experimental conditions there was no evidence for the induction of tumours with bacterial DNA.
SUMMARY: When a culture of the temperature-sensitive DNA mutant Micrococcus radiodurans tsSI is irradiated with a sublethal dose of ultraviolet or ionizing radiation and is plated immediately, all the bacteria give rise, after 36 h incubation, to colonies identical to those derived from unirradiated bacteria. However, when the irradiated population is held at its restrictive temperature (39°C) (restrictive temperature holding) for 3 h before being plated, less than 0.1% of the surviving bacteria give rise to normal colonies, the rest producing, after incubation for 96 h, small malformed colonies. Qualitatively, the same effect is observed when u.v.-irradiated wild-type M. radiodurans is incubated at 39° in the presence of nalidixic acid before plating. Compared with the loss of viability, the loss of normal colony development as a function of the radiation dose is sensitive, having I/e values of 210 ergs/mm2 for u.v. radiation and of 4 to 5 krad for 60Co γ-radiation. These are identical to the radiation dose-response values of a recombination-deficient mutant of M. radiodurans. At first the abnormal colonies consist entirely of giant bacteria but eventually a few bacteria with normal morphology appear and because of their much faster generation time a highly sectored colony results. These colonies can be ‘rescued’ by plating the irradiated bacteria held at 39°C on agar containing pantoyl lactone, their growth being identical to that of unirradiated bacteria. Abnormal colony development is not a general phenomenon in temperature-sensitive mutants of M. radiodurans but occurs in those mutants which are sensitized to radiation when held at 39°C. It is concluded that these abnormal colonies are produced as a result of a defect in a recombination function and that this function is also involved in the regulation of normal cell division.