GENOMIC DNA IN THE FORM OF COMPACT PARTICLES - MORPHOLOGICAL AND BIOLOGICAL ANALYSIS AND OPTICAL-PROPERTIES

Compact DNA particles were obtained by a new method that we developed for isolating high-molecular-mass DNA. The method includes treatment o f interphase cells or metaphase chromosomes with proteinase K when DNA is in the compact state in an aqueous polyethylene glycol-salt medium . The DNA particles obtained from interphase nuclei are globules (appr oximately 8-10 mum in diameter), each containing the genome of an indi vidual cell. The DNA particles obtained from isolated metaphase chromo somes represent the compactly packed DNA of a separate chromosome. Ele ctrophoretic analysis showed that the DNA particles do not contain pro teins. This was also confirmed by electron microscopy: the particles s tudied by means of the protein monolayer technique contained only spre ad DNA molecules. The circular dichroism method demonstrated that the spectra of particles studied in polyethylene glycol-salt solution have a negative band in the 260-290 nm region and an intense positive wing in the 300-400 nm region. The results indicate that inside the partic le the DNA is a left-handed helix. Hence, the obtained preparation con tains purified genomic DNA that probably has an ordered folding.