PHYSICOCHEMICAL CHARACTERIZATION OF A TRANSCRIPTIONALLY ACTIVE DNA-PROTEIN COMPLEX FROM CHLOROPLASTS OF THE FERN AZOLLA-PINNATA

We studied the coefficient of sedimentation in a sucrose density gradi ent, buoyant density in a CsCl gradient, and component composition of the polypeptides of a DNA-protein complex isolated from chloroplasts. It is demonstrated that the complex sediments at a rate of about 150 S . Ultracentrifugation of the formaldehyde-fixed DNA-protein complex in a CsCl gradient revealed two components, with buoyant densities of 1. 63 and 1.57 g.cm-3, respectively. It is hypothesized that two kinds of DNA-protein interactions exist in the DNA-protein complex from chloro plasts of A. pinnata: Some of the proteins are stably associated with chpDNA, while others are less stably associated and separate from the complex in the process of its isolation and purification. The isolated complex was found to contain about 30 polypeptides, with molecular we ights ranging from 14 to 135 kD and including several polypeptides of basic nature. The two major polypeptides of basic nature coincided in electrophoretic mobility with histones H2A+H2B and H3 of wheat embryos .