Intranuclear electrophoresis of the chromatin of living cells.

Intranuclear electrophoresis of living cells under appropriate conditions causes the chromatin and nucleoli to move rapidly into the anodal side of the nucleus. In pig kidney cells, chromatin lengths attached to the nuclear envelope are oriented by the current and freed from surrounding non-oriented chromatin. Individual chromatin strands isolated in this way are often long and have not been subjected to the trauma of isolation from the nucleus. This has allowed us to demonstrate oriented lines of up to 8 chromomeres in a strand, linked by fine single fibres. These chromomeres of chromatin have the same linear dimensions as the bands and interbands of polytene chromosomes. A very wide range of morphology of chromatin is revealed - from lines of nucleosomes in open array, to strands uniformly 25 nm thick. Doublet strands and multiple strands - often embedded in darkly staining material - are also seen. All morphological types may be seen in the same nucleus. Many of the oriented threads appear to be transcriptionally active. The variable morphology of these sites and their relation to peripheral heterochromatin is discussed. Histone nucleosomes are present in these apparently transcriptionally active regions. The method is useful for investigating the relationships between chromatin and the nuclear envelope. Approximately 1500 attachment sites per nucleus are found in these cells. Some nucleoli are attached to the nuclear envelope.