Isolation, Properties and Nucleolytic Degradation of Chromatin from Escherichia coli

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Abstract
A new procedure was developed for the isolation of the chromosome complex, termed chromatin, from E. coli. The bacteria were subjected to low ionic strenth and T4 lysozyme, followed by detergent treatment analogous to that employed for the isolation of eukaryotic chromosomes. The chromatin was an insoluble viscous material which contained approximately equal amounts of DNA and RNA. The protein content of the chromatin was almost 3 times greater than the nucleic acid content. EM revealed that the chromatin was highly condensed, having multiple loops and beaded structures with various diameters. The chromatin could be completely solubilized by both micrococcal nuclease and DNAase I; RNAase had no effect. The initial degradation by micrococcal nuclease resulted in the production of a DNA-protein particle, sedimentation coefficient 10S and an RNA-protein complex of 24S. Further degradation led to a decrease in sedimentation coefficient of the DNA-protein complex, but not of the RNA-protein particle. The peak size of the DNA of the initial DNA-protein particle was .apprx. 2400 bp [base pairs]. The action of micrococcal nuclease also resulted in the production of several discrete RNA species of various sizes. Several low-MW proteins (12,000-27,000) were found in the DNA-protein complex. The DNA-binding protein HU was present in the undigested chromatin; varying amounts of HU were detected in the DNA-protein and RNA-protein particles.

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