Evolution of the Ribosomal DNA Spacers of Drosophila melanogaster : Different Patterns of Variation on X and Y Chromosomes

Length variation of the ribosomal gene spacers of Drosophila melanogaster was studied. Analysis of 47 X chromosomal and 47 Y chromosomal linked rDNA arrays collected from five continents indicates that the arrays on the two chromosomes differ qualitatively. The Y-linked arrays from around the world share little or no similarity for either their overall length or the organization of their spacers. Most of the X-linked arrays do, however, share a major length spacer of 5.1 kb. In addition, those X-linked arrays that have a major 5.1-kb band have similar spacer organization as demonstrated by genomic DNA digestions with several restriction enzymes. These data strongly support the hypothesis that spacer length patterns on only X-linked genes are maintained primarily by natural selection.     

Calcium-sensitive, lipid-binding cytoskeletal proteins of the human placental microvillar region

In this study we describe a group of Ca2+-sensitive proteins located in the microvillar region of the human placental syncytiotrophoblast. By following the distribution of proteins between the particulate and supernatant phases of detergent-solubilized microvilli in the presence of defined concentrations of free Ca2+, we demonstrate a class of proteins of subunit molecular weights 72,000, 69,000, 38,000, 36,000, and 32,000 that associate with both the cytoskeleton and lipid at high concentrations of free Ca2+. These proteins can be released from microvilli using EGTA-containing buffers. Although they do not bind to phenyl-Sepharose, they will bind to phospholipids immobilized on phenyl-Sepharose columns in a Ca2+-dependent manner and show a marked preference for phospholipids with negatively charged headgroups. The results provide evidence for a sequence of events which may occur within the microvillus as the localized concentration of intracellular free Ca2+ rises.     

Crystal structure of cytochrome c peroxidase compound I

We have compared the 2.5-A crystal structure of yeast cytochrome c peroxidase (CCP) with that of its semistable two-equivalent oxidized intermediate, compound I, by difference Fourier and least-squares refinement methods. Both structures were observed at -15 degrees C. The difference Fourier map reveals that formation of compound I causes only small positional adjustments of a few tenths of an angstrom. The map's most pronounced feature is a pair of positive and negative peaks bracketing the heme iron position. Least-squares refinement shows that the iron atom moves about 0.2 A toward the distal side of the heme. No significant difference density is evident near the side chains of Trp-51 or Met-172, each of which has been proposed to be the site of the electron paramagnetic resonance (EPR) active radical in compound I. However, the second most prominent feature of difference density is a negative peak near the side chain of Thr-180, which, according to the results of least-squares refinement, moves by 0.15 A in the direction of Met-230. These observations, together with the results of mutagenesis experiments [Fishel, L. A., Villafranca, J. E., Mauro, J. M., & Kraut, J. (1987) Biochemistry 26, 351-360; Goodin, D. B., Mauk, A. G., & Smith, M. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 1295-1299] in which Trp-51 and Met-172 have been replaced without loss of the EPR radical signal in compound I, lead us to consider the possibility that the radical site lies within a cluster composed of the side chains of Met-230, Met-231, and Trp-191.(ABSTRACT TRUNCATED AT 250 WORDS)     

Symbiotic and competitive properties of motility mutants of Rhizobium trifolii TA1

Non-motile mutants of Rhizobium trifolii defective in either flagellar synthesis or function were isolated by transposon Tn5 mutagenesis. they were indistinguishable from motile control strains in growth in both laboratory media and in the rhizosphere of clover roots. When each non-motile mutant was grown together with a motile strain in continuous culture, the numbers of motile and non-motile organisms remained in constant proportion, implying that their growth rates were essentially identical. When inoculated separately onto clover roots, the mutants and wildtype did not differ significantly in the number of nodules produced or in nitrogen fixing activity. However, when mixtures of equal numbers of mutant and wild-type cells were inoculated onto clover roots, the motile strain formed approximately five times more nodules than the flagellate or non-flagellate, non-motile mutants, suggesting that motility is a factor in competition for nodule formation.     

Quantity and Kinetic Properties of Ribulose 1,5-Bisphosphate Carboxylase in C3, C4, and C3-C4 Intermediate Species of Flaveria (Asteraceae)

The kinetic properties of ribulose 1,5-bisphosphate carboxylase(RuBPC) appear to have been modified during evolution of photosynthesisto adjust to changes in substrate availability. C₄ plants areconsidered to have a higher concentration of CO₂ available toRuBPC than C₃plants. In this study, the K_m(CO₂ and catalyticcapacity (k_cat) of RuBPC and the ratio of RuBPC protein to totalsoluble protein from several Flaveria species, including C₃,C₃-C₄ intermediate, and C₄ species, were determined. The C₃and intermediate species had similar K_m(CO₂) values while theC₄ species on average had higher K_m(CO₂) values. The mean ratioof K_cat/K_m for species of each group was similar, supportingthe hypothesis that changes in K_m and K_cat, are linked. Theallocation of total soluble protein to RuBPC was lowest in theC₄ Flaveria species, intermediate in the C₃-C₄ species, andhighest in the C₃ species. The results suggest that during evolutionof C₄ photosynthesis adjustments may occur in the quantity ofRuBPC prior to changes in its kinetic properties. (Received January 4, 1989; Accepted April 11, 1989)     

Effects of Polyploidy on Photosynthetic Rates, Photosynthetic Enzymes, Contents of DNA, Chlorophyll, and Sizes and Numbers of Photosynthetic Cells in the C(4) Dicot Atriplex confertifolia

Photosynthetic rates, chlorophyll content, and activities of several photosynthetic enzymes were determined per cell, per unit DNA, and per unit leaf area in five ploidal levels of the C₄ dicot Atriplex confertifolia. Volumes of bundle sheath and mesophyll protoplasts were measured in enzymatic digestions of leaf tissue. Photosynthetic rates per cell, contents of DNA per cell, and activities of the bundle sheath enzymes ribulose 1,5-bisphosphate carboxylase (RuBPC) and NAD-malic enzyme per cell were correlated with ploidal level at 99% or 95% confidence levels, and the results suggested a near proportional relationship between gene dosage and gene products. There was also a high correlation between volume of mesophyll and bundle sheath cells and the ploidal level. Contents of DNA per cell, activity of RuBPC per cell, and volumes of cells were correlated with photosynthetic rate per cell at the 95% confidence level. The mesophyll cells did not respond to changes in ploidy like the bundle sheath cells. In the mesophyll cells the chlorophyll content per cell was constant at different ploidal levels, there was less increase in cell volume than in bundle sheath cells with an increase in ploidy, and there was not a significant correlation (at 95% level) of phosphoenolpyruvate carboxylase activity or content and pyruvate,Pi dikinase activity with increase in ploidy. The number of photosynthetic cells per unit leaf area progressively decreased with increasing ploidy from diploid to hexaploid, but thereafter remained constant in octaploid and decaploid plants. Numbers of cells per leaf area were not correlated with cell volumes. The mean photosynthetic rates per unit leaf area were lowest in the diploid, similar in 4×, 6×, and 8×, and highest in the decaploid. The photosynthetic rate per leaf area was highly correlated with the DNA content per leaf area.     

The effect of bromodeoxyuridine and ultraviolet light on 9L rat brain tumor cells

Incorporation of the thymidine analog bromodeoxyuridine (BrdUrd) into DNA increases the sensitivity of a cell to uv light. We have examined the effect of uv light on cell killing and alkaline elution profiles in 9L rat brain tumor cells pretreated with BrdUrd. Combination treatment with BrdUrd and uv irradiation produced a dose enhancement ratio of 3.8 at the 10% survival level compared with uv-radiated control cells; cell killing depended on both the time of treatment and the concentration of BrdUrd used for incubation. Sequential treatment caused single-strand breaks and DNA-protein crosslinks in the portion of DNA containing BrdUrd; uv irradiation alone caused very few strand breaks and no DNA-protein crosslinks. Because of the presence of both lesions in cells treated with BrdUrd and uv light, it was possible to calculate crosslinking factors without using a charging X-ray dose to induce strand breaks, the method commonly used with crosslinking drugs. Results of repair studies suggested that single-strand breaks are repaired more rapidly than are DNA-protein crosslinks.     

Inhibition of Ca2+-induced cytosolic enzyme efflux from skeletal muscle by vitamin E and related compounds.

1. Efflux of an intracellular enzyme (creatine kinase) from normal rat skeletal muscles was induced by treatment with the Ca2+ ionophore A23187. Addition of alpha-tocopherol (230 microM) to the incubation medium was found to significantly diminish this efflux, and this effect was mimicked by alpha-tocopherol acetate, phytol and isophytol, but not by Trolox C (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid). 2. Analysis of muscle cation content has shown that these protective effects of alpha-tocopherol etc. are not due to an inhibition of the Ca2+ accumulating effects of the ionophore. 3. Non-enzymic lipid peroxidation of skeletal-muscle homogenates was found to be inhibited by alpha-tocopherol and Trolox C, partially inhibited by phytol and isophytol, but unaffected by alpha-tocopherol acetate. 4. The activity of lipoxygenase enzymes was partially inhibited by alpha-tocopherol, phytol and isophytol, but not by alpha-tocopherol acetate or Trolox C. 5. Prostaglandin E2 efflux from isolated skeletal muscles was stimulated by treatment with the Ca2+ ionophore, but this was unaffected by alpha-tocopherol treatment.