I. The relative homogeneity of microbial desoxyribonucleic acid. II. The molecular arrangement of the conserved subunits of the desoxyribonucleic acid of Escherichia coli
I. The buoyant density of DNA in a CsCl-density gradient has been shown to depend on its nucleotide composition. The linear relationship has been used to study the distribution of nucleotide compositions among the DNA molecules isolated from a single microbial species. Each microbial DNA has been sh...
| Summary: | I. The buoyant density of DNA in a CsCl-density gradient has been shown to depend on its nucleotide composition. The linear relationship has been used to study the distribution of nucleotide compositions among the DNA molecules isolated from a single microbial species. Each microbial DNA has been shown to be unusually homogeneous relative to the range of compositions found for DNA isolated from different species. The relevance of these findings to current views of the function of DNA in biological systems is discussed.
II. The molecular arrangement of the conserved subunits of E. coli DNA has been investigated by examining molecular fragments of hybrid ^(13)C, ^(15)N E. coli DNA. Two extreme models for the arrangement of subunits, the side-to –side model, and the end-to-end model, were considered. Predictions regarding CsCl-density-gradient distribution for fragments of hybrid DNA were developed for each model. These predictions were based on a theoretical analysis, but utilized pertinent experimental data obtained from a study of unlabelled E. coli DNA. Comparison of theory with experiment indicated that the end-to-end model is incorrect, and set an upper limit to the amount of fully labeled fragments released when hybrid DNA is sonicated.
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