Formation of nascent heteroduplex structures by RecA protein and DNA

E. coli RecA protein promotes homologous pairing in two distinguishable phases: synapsis and strand exchange. With circular single strands (plus strand only) and linear duplex DNA, polarized or unidirectional strand exchange appeared to cause heteroduplex joints to form and grow from a unique end of the duplex DNA. However, a variety of other pairs of substrates appeared to form joint molecules without regard to the polarity of the strands involved. This paradox has been resolved by observations that show that synapsis is fast, nonpolar and sensitive to inhibition by ADP, whereas strand exchange is slow, directional and relatively insensitive to inhibition by ADP. Thus a heteroduplex joint initiated at one end of the duplex DNA grows by continued strand exchange, whereas a joint initiated at the other end dissociates and is unable to start again because accumulating ADP inhibits synapsis. RecA protein appears to form a nascent protein-DNA structure, the RecA synaptic structure, in which at least 100-300 bp in the duplex molecule are held in an unwound configuration and in which the incoming strand is aligned with its complement.     

Combining ability and parental evaluation in five selected clones of sugarcane (Saccharum sp. hybrids)

Summary Five Hawaiian commercial sugarcane (Saccharum sp. hybrids) clones were crossed in a full diallel. Four morphological characters were studied in the progeny: number of millable stalks per plant, stalk diameter, stalk length, and sucrose content. A fifth character, plant volume, was calculated from stalk number, stalk diameter and stalk length. The five selected parental clones were treated as fixed variables in the analysis. General combining ability (gca) was significant for all five characters; specific combining ability (sca) was significant for stalk diameter, stalk length, and plant volume. The variance for gca was large in all progeny populations. However, the variance for sca was large in the progeny of only some clones and/or for some individual characters. Parents were evaluated on the basis of their general combining ability: clone H49-3533 had high gca for sucrose content, while clone H53-5356 had high gca for plant vigor.Published with the approval of the Director as Journal Series Paper No. 455, Experiment Station, Hawaiian Sugar Planters' Association.     

Relaxed circular SV40 DNA as cleavage intermediate of two restriction endonucleases.

We have determined the mode of cleavage of superhelical SV40 DNA (Form I) by restriction endonucleases EcoRI and HpaII at 37 degrees C. By analysis with agarose gel electrophoresis and direct examination with dark field electron microscopy, we found that a large amount of the single-nicked circular DNA (Form II) was produced before the linear SV40 DNA (Form III) appeared. Thus, both restriction enzymes cleave only one strand of the superhelical DNA first. The second cleavage on the complementary strand occurred after a lag period. The first order rate constant for the second cleavage by EcoRI endonuclease was determined and a kinetic reaction scheme for both enzymes is proposed.     

Hyphal anastomosis inPyricularia oryzae cav.

Summary Hyphal anastomosis inPyricularia oryzae occurs naturally in the lower epidermal cells and in the vascular bundles of young lesions on rice. In those cells the invading blast fungus are active. Two hyphal cells lying side by side start an anastomosis by forming two, one from each, very short penetration pegs which are opposite to each other. The cell wall of the pegs and the wall in the vicinity of them are then gradually eliminated and thus form a fusion aperture of 0.2–0.6 m in diameter that is big enough for the migration or exchange of nucleus and cytoplasm between two hyphal cells. The explanation of genetical variation inP. oryzae may be sought on the basis of the ultrastructural evidence of hyphal anastomoses presented in this paper.     

Selection studies in sugarcane (Saccharum sp. hybrids)

Summary An approximate method to determine sample size for the estimation of population variance, ², is given. The estimate of ² is denoted as s² . Based on the assumption of a normal distribution for (s²/²–1), the sample size is approximately equal to 20,000 z² _p,/k²; where z is a standard normal deviate, p is the probability that s² ( 100¦s² – ²¦/²) is less than, or equal to, a critical value k, and k (measured as gDs²) is the desired precision of s² .The expected value of s², with respect to sample size, and the expected cumulative frequencies of s² over sample size for various k values are given. Their goodness of fit to the observed results was satisfactory except for populations that were different from normal. The observed values were taken from a study on four yield components in five sugarcane polycross progenies, grown in two contrasting environments over 2 years in three selection stages.The expected s² was found to be independent of the population coefficient of variance.Research suppoted in part by USDA, ARS, grant #12-14-5001-34. Published with the approval of the Director as Paper No. 412 in the Journal Series of the Experiment Station, Hawaiian Sugar Planters' Association.     

Alcohol dehydrogenases from a facultative methylotrophic bacterium.

Alcohol-oxidizing enzymes of the facultative methylotroph PAR were investigated after growth of the bacteria on methanol and ethanol. During methanol growth only a phenazine methosulfate-linked alcohol dehydrogenase was detected. This enzyme had broad specificity for primary alcohols and was also capable of oxidation of secondary alcohols. It had a molecular weight of 112,000, was composed of two subunits of equal molecular weight, and showed an absolute requirement for ammonium ion for activation. During ethanol growth this enzyme was absent and was replaced by a typical nicotinamide adenine dinucleotide-linked alcohol dehydrogenase of molecular weight 150,000. The latter enzyme also had broad specificity but could not oxidize methanol. This enzyme was not found during methanol growth. These data show that the organism has two distinctly separate mechanisms for oxidation of alcohols.     

PURIFICATION AND PROPERTIES OF CHOLINE ACETYLTRANSFERASE FROM TORPEDO CALIFORNICA

Abstract— Choline acetyltransferase (ChAT), the enzyme responsible for the biosynthesis of acetylcholine in nervous tissue, has been purified to apparent homogeneity from the electric organ of the electric fish Torpedo californica using ion-exchange, gel filtration, and hydroxyapatite chromatography. The final preparation had been purified 8570-fold to a specific activity of 30μmol ACh formed/min/mg protein. The purified protein has a pH optimum of 6.8 (phosphate buffer), is activated by low concentrations (ca. 10 m m ) of ammonium or alkylammonium ions, and is strongly inhibited by a sulfhydryl blocking reagent (DTNB). ChAT has a mol. wt. of 63000 when measured by SDS-polyacrylamide gel electrophoresis or gel filtration.
A new method for the rapid assay of ChAT activity is described in which unreacted substrate ([³H]acetyl-CoA) is removed from reaction mixtures by adsorption to charcoal: some advantages of this technique are discussed.     

Glutamine synthetase. IX. Purification and characterization of the enzyme from sheep spleen.

Glutamine synthetase (L-glutamate: ammonia ligase (ADP-forming), EC 6.3.1.2) has been purified about 550-fold from sheep spleen. The subunit weight of the enzyme is estimated to be 48 000. Sedimentation coefficient determination by density gradient centrifugation gives a value of 15.0 S. The approximate molecular weight calculated from the S value is 378500. In addition, electron micrographs of the enzyme show an "H" shape. Hence, the protein appears to have eight subunits. In sheep spleen, the enzyme resides chiefly in the soluble fraction of the cell. The amino acid composition of the enzyme from spleen shows similarity to that from other sources. The enzyme activity is nearly five times as high in Mg2+ as in Mn2+. ATP inhibits the enzyme; the inhibition is competitive with respect to Mg2+ATP. A number of compounds, such as D-alanine, AMP, creatine phosphate, arsenite in combination with 2,3-dimercaptopropanol, and 2-amino-4-phosphonobutyrate, also inhibit the enzyme. The inhibition by the last compound is competitive with respect to glutamate. D-Glutamate and alpha-methyl-DL-glutamate can serve as substrates in the synthesis reaction, but N-methyl-DL-glutamate cannot. On the other hand, neither D-glutamine nor N-acetyl-L-glutamine can replace L-glutamine as a substrate in the gamma-glutamyl transfer reaction of the enzyme. Inhibition of Mn2+ and ATP and its reversal by Mg2+ have been discussed as a means of regulating the enzyme activity in mammalian tissues.     

稀土元素Pr~(3+)、Nd~(3+)对蚕豆(Vicia feba)叶片原生质膜上Ca~(2+)·Mg~(2+)-ATPase活性的影响

本文介绍用二相分配法制备蚕豆叶片原生质膜上的Ca~(2+)·Mg~(2+)-ATPase,用以研究镧系,稀土离子对此酶活性的影响。初步证实Pr~(3+)、Nd~(3+)对依赖于CaM的以及不依赖于CaM的蚕豆叶片原生质膜上Ca~(2+)·Mg~(2+)-ATPase活性的抑制不是CaM专一的。