scholarly journals Equilibrium Centrifugation

2020 ◽  
Author(s):  
Keyword(s):  
Equilibrium Centrifugation

Disappearance of the covalently closed circular cryptic plasmid PO-2 in Salmonella pullorum MS35 containing F77

1974 ◽  
Vol 20 (4) ◽  
pp. 551-557
Author(s):  
Paul W. Stiffler ◽  
D. E. Schoenhard
Keyword(s):  
Salmonella Typhimurium ◽  
Sucrose Gradient ◽  
Buoyant Density ◽  
Sedimentation Coefficient ◽  
Apparent Effect ◽  
Donor Property ◽  
Circular Dna ◽  
Salmonella Pullorum ◽  
Cryptic Plasmids ◽  
Equilibrium Centrifugation

The physical basis of the donor property of Salmonella pullorum donor strains MS8300, MS830, and MS831 carrying the F77 factor from Salmonella typhimurium was investigated by dye-buoyant density equilibrium centrifugation and zonal centrifugation in neutral sucrose gradients. Centrifugation of the MS8300 and MS831 closed circular DNA material in a 20 to 31% neutral sucrose gradient resulted in a profile having one sharp peak of radioactivity with a sedimentation coefficient of 17 S and a broad peak extending from 65 to 70 S. The 17- and 65-S species were isolated from the isogenic F− strain MS83. These appeared identical with those isolated previously in S. pullorum MS53 as the cryptic plasmids PO-1 and PO-2 respectively. Cosedimentation of differentially labeled F77 DNA and the lysate containing the 65-S and 70-S species suggested that the 70-S species is the autonomous F77 factor in strains MS8300 and MS831. Lysates of MS830 similarly treated produced a profile containing the 17-S molecule and possibly some 70-S molecules but no 65-S molecules. It was concluded that the F77 factor was integrated in most cells and that the covalently closed circular state of PO-2 plasmid was lost. The mutation in the cysE gene of the F77 factor carried by MS831 had no apparent effect on the covalently closed circular nature of PO-2 plasmid, although F77 no longer seemed to mobilize the chromosome from the cysE locus.

Differential order of replication of Xenopus laevis 5S RNA genes

1986 ◽  
Vol 6 (7) ◽  
pp. 2536-2542
Author(s):  
D R Guinta ◽  
L J Korn
Keyword(s):  
Xenopus Laevis ◽  
Rna Replication ◽  
S Phase ◽  
Cold Spring Harbor ◽  
5S Rna ◽  
Expression Model ◽  
Cold Spring ◽  
5S Rna Genes ◽  
Equilibrium Centrifugation ◽  
Rna Genes

In Xenopus laevis there are two multigene families of 5S RNA genes: the oocyte-type 5S RNA genes which are expressed only in oocytes and the somatic-type 5S RNA genes which are expressed throughout development. The Xenopus 5S RNA replication-expression model of Gottesfeld and Bloomer (Cell 28:781-791, 1982) and Wormington et al. (Cold Spring Harbor Symp. Quant. Biol. 47:879-884, 1983) predicts that the somatic-type 5S RNA genes replicate earlier in the cell cycle than do the oocyte-type genes. Hence, the somatic-type 5S RNA genes have a competitive advantage in binding the transcription factor TFIIIA in somatic cells and are thereby expressed to the exclusion of the oocyte-type genes. To test the replication-expression model, we determined the order of replication of the oocyte- and somatic-type 5S RNA genes. Xenopus cells were labeled with bromodeoxyuridine, stained for DNA content, and then sorted into fractions of S phase by using a fluorescence-activated cell sorter. The newly replicated DNA containing bromodeoxyuridine was separated from the lighter, unreplicated DNA by equilibrium centrifugation and was hybridized with DNA probes specific for the oocyte- and somatic-type 5S RNA genes. In this way we found that the somatic-type 5S RNA genes replicate early in S phase, whereas the oocyte-type 5S RNA genes replicate late in S phase, demonstrating a key aspect of the replication-expression model.

scholarly journals Protein - Quinone Interaction: In Vitro Induction of Indirect Antiglobulin Reactions With Methyldopa

Blood ◽  
1974 ◽  
Vol 43 (1) ◽  
pp. 85-97 ◽  
Author(s):  
Arlan J. Gottlieb ◽  
Harold A. Wurzel
Keyword(s):  
Gamma Globulin ◽  
Red Cell ◽  
Prolonged Incubation ◽  
Chemically Modified ◽  
Latex Beads ◽  
Structural Analogues ◽  
In Vitro Induction ◽  
Equilibrium Centrifugation

Abstract Methyldopa-treated gamma globulin can be demonstrated serologically on either the red cell surface or on latex beads by the indirect antiglobulin reaction. The development of a positive antiglobulin reaction was related to methyldopa concentration and the length and temperature of incubation of methyldopa with protein and could be partially inhibited by the addition of albumin to the incubation mixtures. After more prolonged incubation, antiglobulin positivity also developed with plasma-treated with methyldopa. 14C-methyldopa was covalently bound to gamma globulin. Aggregation of gamma globulin following treatment with methyldopa could be demonstrated by both sedimentation velocity and molecular weight determinations employing low-speed equilibrium centrifugation. Protein aggregation was a function of time, temperature, and methyldopa concentration. Detectability by the antiglobulin reaction, the darkening noted in solutions to which methyldopa or hydroquinone had been added, as well as the aggregation of protein was inhibited by a reducing agent which prevented formation of a quinone from the hydroquinone. Some of the immunologically atypical features of the sensitization of red cells by methyldopa or its structural analogues are explicable by the adherence, in vivo, of chemically modified, nonantibody gamma globulin which renders the red cell directly antiglobulin positive.

Sign in / Sign up

Export Citation Format

Share Document