Chromosome Transfer and Recombinant Formation with Deoxyribonucleic Acid Temperature-Sensitive Strains of Escherichia coli

Haploid recombinant yield is reduced in matings conducted at 42.5 C between deoxyribonucleic acid (DNA) temperature-sensitive [dna⁻(TS)] recipients unable to synthesize DNA at 42.5 C and any of the three major donor types (Hfr, F⁺, F′) of Escherichia coli. No such reduction is observed in matings conducted at 42.5 C when the dna⁻(TS) mutation is in the donor parent. Evidence is presented which indicates that chromosome transfer from donors to recipients unable to replicate DNA at 42.5 C during vegetative growth occurs at normal frequencies when the mating is conducted at 42.5 C. It is concluded that some stage in haploid recombinant formation is adversely affected in dna⁻(TS) recipients mated at the temperature restrictive for DNA synthesis.     

Recovery of Colony-Forming Ability and Genetic Marker Activity by UV-Damaged Hemophilus influenzae

The rate of recovery of UV-irradiated Hemophilus influenzae from acriflavine-sensitized loss of colony-forming ability was studied at various acriflavine concentrations, UV doses, and temperatures. This rate (as calculated from an equation based upon certain assumptions) was on the order of 0.07 per minute per cell at 37°C. This did not vary greatly with UV dose or acriflavine concentration, but did with temperature, giving a ΔH‡ of about 16 kcal/mole. In another set of experiments, cells bearing two genetic markers (resistance to 2000 μg/ml streptomycin and to 2.5 μg/ml novobiocin) were irradiated and then incubated without acriflavine. DNA extracts made from samples taken after various periods of incubation time were assayed on antibiotic-sensitive cells using acriflavine to inhibit repair during and following transformation. It was found that both in vivo irradiated markers were reactivated in the donor to approximately the same extent (with a rate constant of 0.04 per minute). This result was in contrast to the results obtained when extracted DNA bearing the same markers was irradiated in vitro and used to transform cells. In this latter case the streptomycin marker was much more sensitive than the novobiocin marker. This difference is interpreted as being due to the mechanics of the transformation system.     

Amino acids as determinants of host preference for the xylem feeding leafhopper,Homalodisca coagulata (Homoptera: Cicadellidae)

Summary Homalodisca coagulata is a highly polyphagous xylem feeder with distinct seasonal patterns in it's selection of host plants. These patterns were examined in relation to the amino acid content of the xylem for four common host species; Lagerstroemia indica, Baccharis halimifolia, Prunus persica, and Prunus salicina. Xylem fluid was collected from each host species at times when numbers of feeding leafhoppers were both low and high. In each case, concentrations of amino acids were greatest when numbers were high. Similarly, comparisons between host species at given times showed that concentrations of amino acids were positively correlated with host selection. In a second study, amino acids of xylem were manipulated by budding scions of a non-preferred host (P. persica) on rootstocks of preferred (P. salinica) and non-preferred (P. persica) hosts. Morphology and phenology of the budded trees were similar to that of the scion species yet the xylem composition of amino acids was primarily dependent on the rootstock. Concentrations of amino acids and the preference of leafhoppers were roughly two-fold greater for scions of the preferred than the non-preferred rootstock. In both studies, amides (glutamine plus asparagine) were the amino acids most highly correlated with host selection. These compounds are the predominant amino acids in xylem fluid, have high nitrogen to carbon ratios, and account for a high percentage of the caloric value in xylem fluid. Many of the less abundant amino acids were positively correlated with host preference, but the correlations were less consistent and correlation coefficients were generally lower.Florida Agricultural Experiment Station Journal Series No. 9672     

Effect of high light on the efficiency of photochemical energy conversion in a variety of lichen species with green and blue-green phycobionts

Exposure to high light induced a quantitatively similar decrease in the rate of photosynthesis at limiting photon flux density (PFD) and of photosystem II (PSII) photochemical efficiency, F_V/F_M, in both green and blue-green algal lichens which were fully hydrated. Such depressions in the efficiency of photochemical energy conversion were generally reversible in green algal lichens but rather sustained in blue-green algal lichens. This greater susceptibility of blue-green algal lichens to sustained photoinhibition was not related to differences in the capacity to utilize light in photosynthesis, since the light-and CO₂-saturated rates of photosynthetic O₂ evolution were similar in the two groups. These reductions of PSII photochemical efficiency were, however, largely prevented in lichen thalli which were fully desiccated prior to exposure to high PFD. Thalli of green algal lichens which were allowed to desiccate during the exposure to high light exhibited similar recovery kinetics to those which were kept fully hydrated, whereas bluegreen algal lichens which became desiccated during a similar exposure exhibited greatly accelerated recovery compared to those which were kept fully hydrated. Thus, green algal lichens were able to recover from exposure to excessive PFDs when thalli were in either the hydrated or desiccated state during such an exposure, whereas in blue-green algal lichens the decrease in photochemical efficiency was reversible in thalli illuminated in the desiccated state but rather sustained subsequent to illumination of thalli in the hydrated state.Abbreviations and Symbols F_o yield of instantaneous fluorescence - F_M maximum yield of fluorescence induced by pulses of saturating light - F_V variable yield of fluorescence - PFD photon flux density (400–700 nm) - PSII photosystem II This work was supported by the Deutsche Forschungsgeneinschaft (Forscherguppe Ökophysiologic and Sonderforschungsbereich 251 of the University of Würzburg) and the Fonds der Chemischen Industrie. W.W.A. gratefully acknowledges the support of a fellowship from the Alexander von Humboldt Foundation. We thank Professor T.G.A. Green for identifying and supplying all of the New Zealand lichen material and Professor F.-C. Czygan for advice concerning the chlorophyll analyses which were performed by Johanna Leisner.     

Mapping in the mouse of the region homologous to the rat growth and reproduction complex (grc)

Offprint requests: J. Klein.     

The carotenoid zeaxanthin and ‘high-energy-state quenching’ of chlorophyll fluorescence

The possibility that zeaxanthin mediates the dissipation of an excess of excitation energy in the antenna chlorophyll of the photochemical apparatus has been tested through the use of an inhibitor of violaxanthin de-epoxidation, dithiothreitol (DTT), as well as through the comparison of two closely related organisms (green and blue-green algal lichens), one of which (blue-green algal lichen) naturally lacks the xanthophyll cycle. In spinach leaves, DTT inhibited a major component of the rapidly relaxing high-energy-state quenching' of chlorophyll fluorescence, which was associated with a quenching of the level of initial fluorescence (F₀) and exhibited a close correlation with the zeaxanthin content of leaves when fluorescence quenching was expressed as the rate constant for radiationless energy dissipation in the antenna chlorophyll. Green algal lichens, which possess the xanthophyll cycle, exhibited the same type of fluorescence quenching as that observed in leaves. Two groups of blue-green algal lichens were used for a comparison with these green algal lichens. A group of zeaxanthin-free blue-green algal lichens did not exhibit the type of chlorophyll fluorescence quenching indicative of energy dissipation in the pigment bed. In contrast, a group of blue-green algal lichens which had formed zeaxanthin slowly through reactions other than the xanthophyll cycle, did show a very similar response to that of leaves and green algal lichens. Fluorescence quenching indicative of radiationless energy dissipation in the antenna chlorophyll was the predominant component of high-energy-state quenching in spinach leaves under conditions allowing for high rates of steady-state photosynthesis. A second, but distinctly different type of high-energy-state quenching of chlorophyll fluorescence, which was not inhibited by DTT (i.e., it was zeaxanthin independent) and which is possibly associated with the photosystem II reaction center, occurred in addition to that associated with zeaxanthin in leaves under a range of conditions which were less favorable for linear photosynthetic electron flow. In intact chloroplasts isolated from (zeaxanthin-free) spinach leaves a combination of these two types of rapidly reversible fluorescence quenching occurred under all conditions examined.Abbreviations DTT dithiothreitol - F₀ (or F₀) yield of instantaneous fluorescence at open PS II reaction centers in the dark (or during actinic illumination) - F_M (or F_M) yield of maximum fluorescence induced by a saturation pulse of light in the dark (or during actinic illumination) - F_V (or F_V) yield of variable fluorescence induced by a saturating pulse of light in the dark (or during actinic illumination) - k _D rate constant for radiationless energy dissipation in the antenna chlorophyll - SV Stern-Volmer equation - PFD photon flux density - PS I photosystem I - PS II photosystem II - Q_A acceptor of photosystem II - q_N coefficient of nonphotochemical chlorophyll fluorescence quenching - q_P coefficient of photochemical chlorophyll fluorescence quenching     

Identification of consensus patterns in unaligned DNA sequences known to be functionally related

We have developed a method for identifying consensus patternsin a set of unaligned DNA sequences known to bind a common proteinor to have some other common biochemical function. The methodis based on a tnatrix representation of binding site patterns.Each row of the matrix represents one of the four possible bases,each column represents one of the positions of the binding siteand each element is determined by the frequency the indicatedbase occurs at the indicated position. The goal of the methodis to find the most significant matrix-i.e. the one with thelowest probability of occurring by chance-out of all the matricesthat can be formed from the set of related sequences. The reliabilityof the method improves with the number of sequences, while thetime required increases only linearly with the number of sequences.To test this method, we analysed 11 DNA sequences containingpromoters regulated by the Escherichia coli LexA protein. Thematrices we' found were consistent with the known consensussequence, and could distinguish the generally accepted LexAbinding sites from other DNA sequences. Received on November 6, 1989; accepted on December 20, 1989