Histone synthesis and deposition in the G1 and S phases of hepatoma tissue culture cells

Hepatoma tissue culture cells were synchronized in G1 and in S phase in order to examine the level of synthesis of different histone types and to determine the rate, timing, and location of their deposition onto DNA. We observe a basal level of synthesis in G1 (5% of that seen in S phase) for H2A.1, H2A.2, H3.2, H2B, and H4. The minor histone variants X and Z are synthesized at 30% of the rate observed in S cells. The rate of synthesis of the ubiquinated histones uH2A.1,2 is not as depressed in G1 cells as seen for H2A.1 and H2A.2. Histones synthesized in G1 are not deposited on the DNA of these cells at equivalent rates. Thus, histones H3.2 and H4 are not deposited significantly until S phase begins, at which time deposition occurs selectively on newly synthesized DNA. The deposition of H2A.1, H2A.2, H2B, X, and Z proceeds in G1; however, it occurs to a 2-4-fold lower extent than seen for the deposition of H1, HMG 14, and HMG 17. The deposition of all histones synthesized in S phase occurs rapidly, but there are variations in the sites of deposition. Thus, newly synthesized H3.1, H3.2, and H4 deposit primarily on newly replicated DNA whereas H2A.1, H2A.2, uH2A.1, 2, and H2B deposit only partially on new DNA (30%) and mostly on old. H1, HMG 14, and HMG 17 are deposited in an apparently fully random manner over the chromatin. To interpret these observations, we propose a model which includes a measure of histone exchange on the chromatin fiber. The model emphasizes the dynamics of histone-histone and histone-DNA interactions in regions of active genes and at replication forks.     

Modification by azocombination of the catalytic properties of ribonucleases

Using pancreatic RNAase and RNAase from Act. rimosus as models, the effect of modification by azocombination on the catalytic properties of enzymes were studied. It was shown that RNAases binding to soluble dextran did not cause any significant changes in their major catalytic properties, when polymeric RNA was used as a substrate. At the same time, the physico-chemical properties of the modified enzymes may result in changes in the catalytic properties in a reaction with low molecular weight substrates. Evidence for this observation can be obtained from the increase in the synthetic activity of modified pancreatic RNAase as compared to the hydrolase activity in the dinucleotide synthesis reaction.     

Characterization of messenger RNA from epimastigotes and metacyclic trypomastigotes of Trypanosoma cruzi

The cell-free translation products of polyribosomal and post-polyribosomal mRNAs from the non-infective epimastigotes and the infective metacyclic trypomastigotes of the parasitic protozoan Trypanosoma cruzi were compared by two-dimensional polyacrylamide gel electrophoresis. The result show that although many polypeptides are conserved, quantitative and qualitative differences are observed between both differentiation stages. The results also indicate the existence of post-polyribosomal mRNAs in equilibrium with polyribosomal counterparts. The immunoprecipitation of the in vitro synthesized polypeptides with chagasic human serum and the serum raised against an 85-kDa glycoprotein (P2-WGA), potentially involved in the process of T. cruzi penetration into mammalian cells, shows that while the chagasic serum recognizes the same 72-kDa, 68-kDa and 46-kDa polypeptides in both differentiation stages, the anti-P2-WGA serum immunoprecipitates a single 48-kDa polypeptide from in vitro translation products of metacyclic trypomastigotes.     

Periodicity in the rise and fall of the numbers of the principal Staphylococcus aureus phage groups

The results of the phage typing of 5, 168 Staph. aureus strains isolated in a surgical hospital between 1959 and 1977 are analyzed for each year of this period. The wave of increase in the number of staphylococci belonging to phage group II which began, as discovered in this study, in 1965 and still showed no tendency towards decrease in 1977, as well as the periodicity of rises and falls in the number of staphylococci belonging to phage groups I and III are discussed and compared with the data contained in the literature. The authors come to the conclusion that Staph. aureus is subject to wave-like rises and falls in the number of strains belonging to the main phage groups of the species, and among them the strains belonging to phage groups I and III seem to be inversely related in respect of rises and falls in number, such changes occurring periodically at an interval of 10-12 years, while in the strains belonging to phage group II changes in number occur at a slower rate. The constant account of the percentage of phage groups I, II and III is recommended to ensure rational antibiotic therapy.     

Production of tetanolysin preparations and characteristics of their properties

As the result of the study of tetanolysin-producing Clostridium tetani strains, their populations have been found to be markedly heterogeneous with respect to the hemolytic activity of clone cultures. On the basis of normal and dialyzed cultures of selected variants with maximum activity the preparations of tetanolysin have been obtained, and their hemolytic activity and antigenic properties have been studied. Antihemolytic rabbit sera have also been obtained and characterized. Partially purified preparations of tetanolysin with high hemolytic activity have been obtained by the fractionation of C. tetani dialyzed cultures with ammonium sulfate.     

Fast, efficient and selective deprotection of the tert-butoxycarbonyl (Boc) group using HCl/dioxane (4 m).

Fast, efficient and selective deprotection of the tert-butoxycarbonyl (Boc) group of various amino acids and peptides was achieved by using hydrogen chloride (4 m) in anhydrous dioxane solution for 30 min at room temperature. In the cases studied in our laboratory, this protocol provided superior selectivity to deprotect Nalpha-Boc groups in the presence of tert-butyl esters and tert-butyl ethers, including thio-tert-butyl ethers, but not phenolic tert-butyl ethers.     

New Gene Crt(Curly Roots) Controlling Pea (Pisum sativum L.) Root Development

Using ethyl methane sulfonate (EMS) treatment of the seeds ofline SGE, a new mutant of pea (Pisum sativum L.) with alterationsin root development was obtained. The mutant phenotype dependson the density of the growth substrate: on sand (a high densitysubstrate) the mutant forms a small compact curly root systemwhereas on vermiculite (a low density substrate) differencesbetween the root systems of the mutant and wild type plantsare less pronounced. Genetic analysis revealed that the mutantcarries a mutation in a new pea gene designedcrt (curly roots).Gene crt has been localized in pea linkage group V. The mutantline named SGEcrt showed increased sensitivity to exogenousauxin and an increased concentration of endogenous indole-3-aceticacid (IAA) in comparison with the wild type line SGE. Copyright2000 Annals of Botany Company Pisum sativum L., root development, garden pea mutant, curly roots, auxin, environmental stimulus response     

Effect of precursors on biosynthesis of monensins A and B

Precursors of monensins (acetate, propionate, butyrate, isobutyrate) affect the total production and the relative proportion of monensins A and B. Addition of propionate into the fermentation medium causes a prevalence of monensin B whereas butyrate and isobutyrate stimulate the production of monensin A and suppress the production of monensin B.