ABSTRACT
The effects of vitamin E, vitamin B2 and selenite on DNA single strand breaks induced by Na2CrO4 were examined by alkaline elution. Incubation of Chinese hamster V-79 cells with alpha-tocopherol succinate (vitamin E) for 24 h prior to exposure to Na2CrO4 resulted in a decrease of DNA breaks produced by this compound. However, similar pretreatment with riboflavin (vitamin B2) or Na2SeO3 resulted in an enhanced formation of breaks induced by Na2CrO4. Pretreatment with Na2SeO3 resulted in increased levels of glutathione in these cells while levels of glutathione remained the same with vitamin E or vitamin B2. These results suggest that Na2CrO4 induced DNA breaks appear to be mediated by the formation of free radicals and/or cellular reductive metabolism.
Subject(s)
Chromates/toxicity , DNA Damage , Riboflavin/pharmacology , Selenium/pharmacology , Sodium Compounds , Vitamin E/pharmacology , Animals , Cells, Cultured , Cricetinae , Free Radicals , Glutathione/analysis , Selenious AcidABSTRACT
Twenty-four clones of EcoR1-restricted, 340-base pair (bp) DNA derived from human DNA have been sequenced and compared to a published consensus sequence for this family. No two clones were found to have identical sequences; the clones studied differed from the consensus sequence in as few as 1 or as many as 41 sites. On the average in these clones, a 5.2% divergence from exact homology was found, with 1 of 10 of the site variations being "nonrandom," i.e., cases in which five or more clones had the same nucleotide substitution at that site (viz., 53, 124, 126, 138, 152, and 157). At site 157, for example, 16 of the 24 clones differed from the reference sequence. Positions and their respective changes, as compared to the consensus sequence, are summarized. Variations are discussed with relation to possible functions for these sequences.
Subject(s)
DNA/genetics , Repetitive Sequences, Nucleic Acid , Base Sequence , DNA Restriction Enzymes/metabolism , Deoxyribonuclease EcoRI , HumansABSTRACT
The natural DNA sequence of bacteriophage, phi X174, when analyzed as a "text" of dinucleotides, is shown to display an easily detectable degree of non-randomness by the distribution of values of dinucleotide self-information along the sequence. Self-information corresponding to occurrences of dinucleotides separated by a single nucleotide is found to be somewhat higher than the values which precede or follow it for every third nucleotide position along the sequence. Consequently autocorrelation coefficients of these values display a strong periodicity and harmonic analysis of the values shows a spike at a value of 3. Self-information autocorrelation periodicity is used as a test of the effect of randomizing portions of the sequence. Any one or two of the three nucleotides in each triplet of the sequence can be chosen at random without losing dinucleotide self-information periodicity except when both the 1st and 3rd nucleotide of all of the triplets in the major phi X174 protein reading frame are randomized. Periodicity is also lost when sequences are generated by randomizing triplets. Autocorrelation and harmonic analysis also indicate other less marked periodic features of dinucleotide self-information values of the nature sequence; non-random features are suggested at periods of 12, 20 and 24 nucleotides.
Subject(s)
Bacteriophage phi X 174/analysis , DNA, Viral , Oligonucleotides/analysis , Base Sequence , Dinucleoside PhosphatesSubject(s)
Acridines/pharmacology , DNA, Neoplasm/metabolism , Leukemia L1210/metabolism , Acridines/administration & dosage , Animals , Centrifugation, Density Gradient , DNA, Single-Stranded/metabolism , Hydrogen-Ion Concentration , Leukemia L1210/drug therapy , Mice , Mice, Inbred DBA , Phenylenediamines/administration & dosage , Phenylenediamines/pharmacology , Time FactorsABSTRACT
The effects of various modifications on the beta subunit of lutropin have been studied using the binding characteristics of the reconstituted hormone in the rat testicular radioligand assay. Conditions for iodinating lutropin and lutropin derivatives were determined which resulted in 15 per cent specific binding when tested immediately and retention of 6 to 7 per cent specific binding even after storage for 6 months. Acetimidinyl, acetyl, and carbamyl derivatives of the beta subunit were prepared and combined with unmodified alpha subunit to form reconstituted lutropin. Modification of the beta subunit was shown to have no effect on the time course of binding to testicular receptors or, with one exception, on the extent of receptor saturation. Very high concentrations of lutropin reconstituted with acetylated beta subunit showed an anomalous binding behavior. Scatchard plots of the binding data support the view that the native hormone has a unique receptor affinity which is irreversibly disrupted by separation of subunits and that derivatization of the beta subunit does not alter this parameter further. These data also suggest that there are no significant differences in the amino groups modified on the beta subunit. Competition and preincubation tests for receptor sites that reacted only with modified lutropin and not with the native hormone were negative.
