Male recombination with single and homologous P elements in Drosophila melanogaster

It has previously been shown that, in the presence of a source of P element transposase, male recombination in Drosophila melanogaster is induced at a rate of about 1% in the region of a single P[CaSpeR] element. This paper shows that recombinant chromosomes retain unaltered P[CaSpeR] elements at the original site in a high proportion of cases. This result is incompatible with a simple model in which recombination occurs by resolution of a Holliday junction following P element excision and repair. It has also previously been shown that homozygous regions containing a P element produce male recombination levels of 10–20%, an order of magnitude higher than that given by a single element. This paper shows that reciprocal recombinant chromosomes retaining P[CaSpeR] elements can be combined to produce similarly high levels of recombination. This result potentially allows for recombinant chromosomes from homologous recombination to be analysed at the molecular level in the region of the inserted element.     

Electric fields affect the orientation of cortical microtubules and cell expansion in pea callus

Summary Cortical microtubules in callus derived fromPisum sativum roots form parallel arrays within cells but are randomly oriented across the tissue. These arrays align perpendicular to the direction of an applied electric field of 6 mV per cell. Application of a field of 6 mV per cell for 4 days resulted in the co-ordinated expansion of cells parallel to the field direction. Cortical microtubule arrays were still aligned perpendicular to the applied field 24 h after removal of the field. The imposition of a field to callus after the removal of cortical microtubules by oryzalin and in the presence of the herbicide resulted in the orientation of recovering microtubules perpendicular to the direction of the field, indicating that microtubules are not directly involved in the detection of the field.Abbreviations EGTA ethylene glycol-bis (-aminoethyl ether) N,N,N-tetraacetic acid - FITC fluorescein isothiocyanate - MSB microtubule stabilising buffer - PIPES piperazine-N,N-bis(2-ethanesulphonic acid) - oryzalin 3,5-dinitro-N⁴,N⁴ dipropylsulphanil-amide     

Male recombination with single and homologous P elements in Drosophila melanogaster

It has previously been shown that, in the presence of a source of P element transposase, male recombination in Drosophila melanogaster is induced at a rate of about 1% in the region of a single P[CaSpeR] element. This paper shows that recombinant chromosomes retain unaltered P[CaSpeR] elements at the original site in a high proportion of cases. This result is incompatible with a simple model in which recombination occurs by resolution of a Holliday junction following P element excision and repair. It has also previously been shown that homozygous regions containing a P element produce male recombination levels of 10–20%, an order of magnitude higher than that given by a single element. This paper shows that reciprocal recombinant chromosomes retaining P[CaSpeR] elements can be combined to produce similarly high levels of recombination. This result potentially allows for recombinant chromosomes from homologous recombination to be analysed at the molecular level in the region of the inserted element.     

Weak coordination among petiole,leaf, vein,and gas‐exchange traits across Australian angiosperm species and its possible implications

Close coordination between leaf gas exchange and maximal hydraulic supply has been reported across diverse plant life forms. However, it has also been suggested that this relationship may become weak or break down completely within the angiosperms. We examined coordination between hydraulic, leaf vein, and gas‐exchange traits across a diverse group of 35 evergreen Australian angiosperms, spanning a large range in leaf structure and habitat. Leaf‐specific conductance was calculated from petiole vessel anatomy and was also measured directly using the rehydration technique. Leaf vein density (thought to be a determinant of gas exchange rate), maximal stomatal conductance, and net CO₂ assimilation rate were also measured for most species (n = 19–35). Vein density was not correlated with leaf‐specific conductance (either calculated or measured), stomatal conductance, nor maximal net CO₂ assimilation, with r² values ranging from 0.00 to 0.11, P values from 0.909 to 0.102, and n values from 19 to 35 in all cases. Leaf‐specific conductance calculated from petiole anatomy was weakly correlated with maximal stomatal conductance (r² = 0.16; P = 0.022; n = 32), whereas the direct measurement of leaf‐specific conductance was weakly correlated with net maximal CO₂ assimilation (r² = 0.21; P = 0.005; n = 35). Calculated leaf‐specific conductance, xylem ultrastructure, and leaf vein density do not appear to be reliable proxy traits for assessing differences in rates of gas exchange or growth across diverse sets of evergreen angiosperms.     

Importance of alignment between local DC magnetic field and an oscillating magnetic field in responses of brain tissue in vitro and in vivo

The frequency dependence of the electric and magnetic (EM)-field-induced release of calcium ions from an in vitro brain tissue preparation has been shown to be a function of the density of the local DC magnetic field (Bdc). In this study, we demonstrate that the relative orientation of the Bdc and the magnetic component (Bac) of a 315-Hz EM signal (15 Vrms/m and 61 nTrms) are crucial for the induced release to be observed. The induced release occurs only when the Bdc and the Bac are perpendicular, and not when they are parallel. This finding is consistent with a magnetic resonance-like transduction mechanism for the conversion of EM energy into a physicochemical change, and contrasts with the requirement for parallel Bdc and Bac components in the diatom-mobility experiments of Smith et al. A review of the exposure conditions in the rat behavioral experiments conducted by Thomas et al. identifies unhydrated calcium and zinc ions as alternatives to lithium ions as candidates for interaction under parallel magnetic-field orientations but fails to reject perpendicular orientations as an alternative basis for the phenomenon. Investigators that attempt to confirm the rat behavioral experiments should be aware of the conflicting exposure conditions that can be assumed to be operative, and they should design their experiments to test all conditions accordingly.     

Inheritance of low-level resistance to penicillin, tetracycline, and chloramphenicol in Neisseria gonorrhoeae.

The genetics of low-level resistance to penicillin and other antibiotics in a clinical isolate and a multistep laboratory mutant of Neisseria gonorrhoea was studied by transformation. Mutations at three loci affected sensitivity to penicillin. Mutation at penA resulted in an eightfold increase in resistance to penicillin without affecting response to other antimicrobial agents. Mutation at ery resulted in a two- to fourfold increase in resistance to penicillin and similar increases in resistance to many other antibiotics, dyes, and detergents. Mutation at penB resulted in a fourfold increase in resistance to penicillin and tetracycline, the phenotypic expression of which was dependent on the presence of mutation at ery. The cumulative effect of mutations at penA, ery, and penB was an approximate 128-fold increase in penicillin resistance, to a minimum inhibitory concentration of 1.0 mug/ml. Low-level resistance to tetracycline or chloramphenicol was due to similar additive effects between mutations at the nonspecific ery and penB loci and a locus specific for resistance to each drug (tet and chl, respectively). No evidence was found for penicillinases or other drug-inactivating enzymes.     

High-frequency conjugal transfer of a gonococcal penicillinase plasmid.

Gonococci containing a 24 X 10(6)-dalton conjugal plasmid were able to mobilize for transfer a smaller, non-self-transmissible penicillinase (Pcr) plasmid with high frequency under appropriate conditions. In some strains, over 10% of donor colony-forming units transferred the Pcr plasmid in a mating of less than 2 h, which suggests that the conjugal system was naturally derepressed. Colony-opacity variants containing different quantities of an approximately 28,000-dalton outer membrane protein were altered in their ability to act as conjugal donors and recipients. Maximal transfer of the Pcr plasmid was observed between transparent donors and recipients, lacking appreciable amounts of the 28,000-dalton protein. Under conditions of high-frequency Pcr plasmid mobilization, no conjugal mobilization of chromosomal markers could be discerned.     

Function of calmodulin in postsynaptic densities. II. Presence of a calmodulin- activatable protein kinase activity

Because the calmodulin in postsynaptic densities (PSDs) activates a cyclic nucleotide phosphodiesterase, we decided to explore the possibility that the PSD also contains a calmodulin-activatable protein kinase activity. As seen by autoradiographic analysis of coomassie blue-stained SDS polyacrylamide gels, many proteins in a native PSD preparation were phosphorylated in the presence of [γ-(32)P]ATP and Mg(2+) alone. Addition of Ca(2+) alone to the native PSD preparation had little or no effect on phosphorylation. However, upon addition of exogenous calmodulin there was a general increase in background phosphorylation with a statistically significant increase in the phosphorylation of two protein regions: 51,000 and 62,000 M(r). Similar results were also obtained in sonicated or freeze thawed native PSD preparations by addition of Ca(2+) alone without exogenous calmodulin, indicating that the calmodulin in the PSD can activate the kinase present under certain conditions. The calmodulin dependency of the reaction was further strengthened by the observed inhibition of the calmodulin-activatable phosphorylation, but not of the Mg(2+)-dependent activity, by the Ca(2+) chelator, EGTA, which also removes the calmodulin from the structure (26), and by the binding to calmodulin of the antipsychotic drug chlorpromazine in the presence of Ca(2+). In addition, when a calmodulin-deficient PSD preparation was prepared (26), sonicated, and incubated with [γ-(32)P]ATP, Mg(2+) and Ca(2+), one could not induce a Ca(2+)-stimulation of protein kinase activity unless exogenous calmodulin was added back to the system, indicating a reconstitution of calmodulin into the PSD. We have also attempted to identify the two major phosphorylated proteins. Based on SDS polyacrylamide gel electrophoresis, it appears that the major 51,000 M(r) PSD protein is the one that is phosphorylated and not the 51,000 M(r) component of brain intermediate filaments, which is a known PSD contaminant. In addition, papain digestion of the 51,000 M(r) protein revealed multiple phosphorylation sites different from those phosphorylated by the Mg(2+)-dependent kinase(s). Finally, although the calmodulin-activatable protein kinase may phosphorylate proteins I(a) and I(b), the cyclic AMP-dependent protein kinase, which definitely does phosphorylate protein I(a) and I(b) and is present in the PSD, does not phosphorylate the 51,000 and 62,000 M(r) proteins, because specific inhibition of this kinase has no effect on the levels of the phosphorylation of these latter two proteins.     

Structure of rapidly frozen gap junctions

The structure of gap junctions in the rabbit ciliary epithelium, corneal endothelium, and mouse stomach and liver was studied with the freeze-fracturing technique after rapid freezing to near 4 degrees K from the living state. In the ciliary epithelium, the connexons were randomly distributed, separated by smooth membrane matrix. In the corneal endothelium, both random and crystalline arrangements of the connexons were observed. In the stomach and liver, the connexons were packed but not crystalline. Experimental anoxia or lowered pH caused crystallization of the connexons within 20-30 min. In the ciliary epithelium, the effects of prolonged anoxia or low pH could not be reversed . In addition, invaginated or annular gap junctions increased in number, but their connexons were usually distributed at random. Rapid freezing thus demonstrates that gap junctions of different tissues are highly pleiomorphic in the living state, and this may explain their variations in structure after chemical fixation. The slow time-course and irreversibility of the morphological changes induced by prolonged anoxia or low pH suggest that connexon crystallization may be a long-term consequence rather than the morphological correlate of the switch to high resistance.     

Amino Acid Transport in Suspension-cultured Plant Cells: II. CHARACTERIZATION OF l-LEUCINE UPTAKE

l-Leucine (l-Leu) transport into suspension cultured Nicotiana tabacum L. cv. Wisconsin 38 cells has been investigated. Cells were batch-cultured and routinely assayed 3.5 to 4 days after subculturing. Uptake rates were measured over the concentration range of 10 micromolar to 150 millimolar. Kinetic analysis of the uptake rates indicated that uptake was multiphasic with three saturable phases and one unsaturable phase. The three saturable phases which occur in the concentration ranges of 10 to 40 micromolar, 50 to 100 micromolar, and 0.2 to 5.0 millimolar exhibited the following characteristics; (a) phases were energy-dependent as shown by 84 to 94% inhibition of uptake rates by metabolic inhibitors; (b) phases exhibited broad pH optima between 3.0 and 5.5; (c) phases showed stereospecificity for l-Leu; (d) over a 12-hour incubation period, phases concentrated l-Leu 43, 90, and 10 times when the initial l-Leu concentration was 20 micromolar, 100 micromolar, and 1.0 millimolar, respectively; (e) phases had K(m) values of 17.6 micromolar, 60.1 micromolar, and 1.38 millimolar, respectively; and (f) in the temperature range of 17 to 27 C phases had Q(10) values of 2.1, 1.4, and 1.4, respectively. l-Leu uptake in the three saturable phases was inhibited by a 20-fold higher concentration of 18 other amino acids; phenylalanine, alanine, and methionine were the most effective inhibitors, whereas aspartic acid, asparagine, histidine, and arginine were the least effective. The nonsaturable phase which was responsible for increases in the uptake rate above 5.0 mm appeared to be primarily diffusional since it was minimally influenced by metabolic inhibitors and had a Q(10) of 1.3.