In this paper we have studied the effect of raising the intracellular EF‐Tu concentration on the expression of tufB. To this aim cells were transformed with multicopy plasmids carrying either tufA or Show moreIn this paper we have studied the effect of raising the intracellular EF‐Tu concentration on the expression of tufB. To this aim cells were transformed with multicopy plasmids carrying either tufA or tufB. The intracellular EF‐Tu concentrations were determined by the specific immunoelectrophoresis assay described in the preceding paper in this journal. We have cloned the tufA gene in a plasmid, containing the powerful major leftward promoter (Pl) of phage λ Transcription from Pl can be repressed at low temperature by a temperature‐sensitive repressor and acitvated by heat induction. Cloning occurred in two orientations in a single EcoRI site about 150 base pairs downstream of Pl. Cells carrying either plasmid were shown to contain an almost doubled amount of EF‐Tu at temperatures from 28°C to 37°C. This indicates that transcription of tufA can proceed from a possible binding site for RNA polymerase on these cloned fragments. The EF‐Tu level was further increased to about 30% of total cellular protein after a temperature shift from 37°C to 43°C. The multicopy plasmid pTuB1 described by Miyajimaet al. [FEBS Lett. 102, 207–210 (1979)] and a derivative (pTuBo, compare preceding paper in this journal) were used to study the expression of both chromosomal and plasmid‐borne tufB. Transformation with either plasmid raised the intracellular EF‐Tu concentration by 30–60% depending on the nutritional conditions. Suppression of tufB expression was observed when the intracellular level of EF‐Tu increased after transformation with all plasmids mentioned above. The results are in accord with the concept that EF‐Tu acts as an autogenous feedback inhibitor involved in the regulation of tufB. Show less
The yield of the triplet state of the primary electron donor of Photosystem I of photosynthesis (PT-700) and the characteristic parameters (g value, line shape, saturation behavior) of the ESR... Show moreThe yield of the triplet state of the primary electron donor of Photosystem I of photosynthesis (PT-700) and the characteristic parameters (g value, line shape, saturation behavior) of the ESR signal of the photoaccumulated intermediary acceptor A have been measured for two types of Photosystem I subchloroplast particles: Triton particles (TSF 1, about 100 chlorophyll molecules per P-700) that contain the iron-sulfur acceptors FX, FB and FA, and lithium dodecyl sulfate (LDS) particles (about 40 chlorophyll molecules per P-700) that lack these iron-sulfur acceptors. The results are: (i) In Triton particles the yield of PT-700 upon illumination is independent of the redox state of A and of FX,B,A and is maximally about 5% of the active reaction centers at 5 K. The molecular sublevel decay rates are kx = 1100 s−1 ± 10%, ky = 1300 s−1 ± 10% and kz = 83 s−1 ± 20%. In LDS particles the triplet yield decreases linearly with concentration of reduced intermediary acceptors, the maximal yield being about 4% at 5 K assuming full P-700 activity. (ii) In Triton particles the acceptor complex A consists of two acceptors A0 and A1, with A0 preceding A1. In LDS particles at temperatures below −30°C only A0 is photoactive. (iii) The spin-polarized ESR signal found in the time-resolved ESR experiments with Triton particles is attributed to a polarized P-700-A−1 spectrum. The decay kinetics are complex and are influenced by transient nutation effects, even at low microwave power. It is concluded that the lifetime at 5 K of P-700A0A−1 must exceed 5 ms. We conclude that PT-700 originates from charge recombination of P-700A−0, and that in Triton particles A0 and A1 are both photoaccumulated upon cooling at low redox potential in the light. Since the state P-700AF−X does not give rise to triplet formation the 5% triplet yield in Triton particles is probably due to centers with damaged electron transport. Show less
The system of land use as practised in the mid-20th century was as follows: the fields, called the lands, were found outside the village at distances varying from 5 to 50 km. Every household... Show moreThe system of land use as practised in the mid-20th century was as follows: the fields, called the lands, were found outside the village at distances varying from 5 to 50 km. Every household maintained a temporary shelter at the lands for use during the agricultural season. Beyond the zone of fields were the grazing areas, the cattle posts. Now the large nucleated villages are undergoing some radical changes as a result of permanent migrations to the lands and the cattle posts. This study investigates, with special reference to the Kweneng district: 1) why some people are now settling parmanently at the lands instead of migrating seasonally between their fields and villages; 2) what the implications of their decision to live at the lands are for the rural economy and society, viz: the provision of social services and trading and chieftaincy and local government. Show less
