Osmotic regulation of transcription: induction of the proU betaine transport gene is dependent on accumulation of intracellular potassium

The proU locus, which encodes a high-affinity betaine transport system, and the kdp operon, which encodes a potassium transport system, are the principal osmoresponsive genes in Escherichia coli and Salmonella typhimurium. The kdp operon is known to be induced in response to changes in cell turgor. We have investigated the control of proU expression and shown that it differs from that of kdp in a number of fundamental ways. Rather than responding to changes in turgor, proU expression is principally determined by the intracellular accumulation of potassium ions. Potassium and betaine were shown to play distinct osmoprotective roles. Potassium serves as the principal osmoprotectant and is accumulated in response to low-level osmotic stress to restore turgor. As external osmolarity is increased to a level at which the corresponding increase in internal potassium concentrations is potentially deleterious to enzyme function, betaine (when available) is accumulated in preference to potassium. The different mechanisms of proU and kdp regulation reflect the different physiological roles of these two osmoprotectants.     

Transition from somatic to meiotic pairing and progressional changes of the synaptonemal complex in spermatocytes of Aedes aegypti

Aedes aegypti spermatocytes were reconstructed from electron micrographs. The species has tight somatic pairing of the chromosomes, and there are therefore no classical leptotene and zygotene stages, but rather a gradual transition from somatic pairing to meiotic pairing (= pachytene). The term prepachytene has been used for the transitory stage. The first visible sign of impending meiosis was a reorganization of the chromatin, which resulted in the formation of spaces (synaptic spaces) in the chromatin, about the width of the synaptonemal complexes (SCs). Diffuse material, possibly precursor material for the SC, was present in the spaces. Later short pieces of complex were formed throughout the nucleus. Late prepachytene, pachytene, and diplotene complexes were reconstructed. Each chromosome occupied a separate region of the nucleus. The complexes became progressively shorter from prepachytene (maximum complement length 289 m) to diplotene (175 m). The thickness of the SCs increased from prepachytene to pachytene and probably decreased again during diplotene. At the beginning of diplotene the lateral elements (LEs) separated, and the single LEs became two to three times thicker than the LEs of the SC. The centromeres were at all stages attached to the nuclear membrane, whereas the telomeres were free in the nucleoplasm during pachytene and diplotene. A heterochromatic marker was present on chromosome 1 near the sex determining locus, and a diffuse marker on chromosome 3 near the nucleolus organizer region. After breakdown of the complexes, polycomplexes were present in the nucleus.     

Seasonal Bacterial Production in a Dimictic Lake as Measured by Increases in Cell Numbers and Thymidine Incorporation

Rates of primary and bacterial production in Little Crooked Lake were calculated from the rates of incorporation of H¹⁴CO₃⁻ and [methyl-³H]thymidine, respectively. Growth rates of bacteria in diluted natural samples were determined for epilimnetic and metalimnetic bacterial populations during the summers of 1982 and 1983. Exponential growth was observed in these diluted samples, with increases in cell numbers of 30 to 250%. No lag was observed in bacterial growth in 14 of 16 experiments. Correlation of bacterial growth rates to corresponding rates of thymidine incorporation by natural samples produced a conversion factor of 2.2 × 10¹⁸ cells produced per mole of thymidine incorporated. The mass of the average bacterial cell in the lake was 1.40 × 10⁻¹⁴ ± 0.05 × 10⁻¹⁴ g of C cell⁻¹. Doubling times of natural bacteria calculated from thymidine incorporation rates and in situ cell numbers ranged from 0.35 to 12.00 days (median, 1.50 days). Bacterial production amounted to 66.7 g of C m⁻² from April through September, accounting for 29.4% of total (primary plus bacterial) production during this period. The vertical and seasonal distribution of bacterial production in Little Crooked Lake was strongly influenced by the distribution of primary production. From April through September 1983, the depth of maximum bacterial production rates in the water column was related to the depth of high rates of primary production. On a seasonal basis, primary production increased steadily from May through September, and bacterial production increased from May through August and then decreased in September.     

The effect of Cd2+ on the biosynthesis of chlorophyll in leaves of barley

The effect of cadmium on the biosynthesis of chlorophyll has been investigated in the leaves of dark-grown seedlings of barley ( Hordeum vulture L. cv. Proctor). Cd2+ inhibited the production of chlorophyll by affecting 1) the synthesis of 5-aminolacvulinic acid and 2) the protoehlorophyllide reductase ternary complex with its substrates. Cd2+ had no effect on the constituent enzymes that catalyse the synthesis of free protoehlorophyllide from 5-aminolaevulinic acid. The results obtained are consistent with Cd2+ inhibiting the formation of chlorophyll by reacting with essential thiol groups in both the protochlorophyllide reductase protein and the enzyme(s) involved in the light dependent synthesis of 5-aminolaevulinic acid.     

Testosterone metabolic clearance rate and production rate in the male infant rhesus monkey

The male infant rhesus monkey (Macaca mulatta) undergoes a period of testicular activation similar to that seen in the human infant. Plasma testosterone (T) concentrations rise after birth, reaching levels of about 500 ng/dl at 1-3 mo of age and then fall to approximately 50 ng/dl at 60 mo. The plasma T metabolic clearance rates (MCRT) and production rates (PRT) were measured in two rhesus infants at 1 and 6 mo of age to determine the mechanism of the observed increase in plasma T. While there was little change in the MCRT between 1 and 6 mo, PRT was much higher at 1 mo than at 60 mo of age. These observations are consistent with the hypothesis that the increased plasma testosterone levels in infant rhesus monkeys reflect an increased production of testosterone rather than an altered metabolic disposition of the hormone.     

Roles of the trkB and trkC gene products of Escherichia coli in K+ transport

Mutations at the trkB and trkC loci of Escherichia coli produce an abnormal efflux of K+. The mutations are partially dominant in diploids and revert frequently by what appears to be intragenic suppression to the null state. The mutations can be reverted by insertion of Tn10 into the mutated gene, and spontaneous revertants are fully recessive to the mutant allele in diploids. K+ efflux produced by NEM* and by DNP* persists in strains with presumed null mutations at either locus, indicating neither gene product is the primary target for the effect of these inhibitors on K+ efflux. The results are consistent with the view that trkB and trkC encode independent systems for K+ efflux. Mutations at these loci alter regulation of the process so that K+ efflux occurs inappropriately. A second mutation to the null state abolishes this abnormal K+ efflux. These genes may encode K+/H+ antiporters, an activity postulated to mediate K+ efflux and demonstrated to exist in E. coli and other bacteria.     

Evidence for an increased rate of choline efflux across erythrocyte membranes in Alzheimer's disease

Alzheimer's disease (AD), the major dementing disorder of the elderly, is associated with cholinergic neuronal loss and decreased activity of choline acetyl-transferase (CAT). Previous biophysical studies had suggested an altered conformation of membrane proteins in AD erythrocyte ghosts. Since erythrocytes have a choline transport system and cholinergic neurons are implicated in AD, the present experiments were undertaken to determine if the efflux rate of [¹⁴C]choline was altered in AD erythrocytes. The mean efflux rate constant was highly significantly increased (P<0.01) by greater than 25% in 9 drug-free AD patients compared to 9 sex-matched, drug-free controls of similar age. These results are discussed in terms of potential molecular mechanisms to account for cholinergic neuronal loss in AD.