Developmental transitions between chromatin-bound and soluble RNA polymerase subspecies in the soybean hypocotyl.

RNA polymerase enzymes isolated from soybean hypocotyl tissue during successive developmental stages (2-8 days old) have been fractionated by Sephadex column isoelectric focusing. Both the enzymes bound to chromatin and those enzymes free in the soluble phase were investigated during development with respect to their distribution within these two pools. All observed activites were classified according to their alpha-amanitin sensitivity and isoelectric points. Two Class I subspecies (Ia, Ib) and two Class III subspecies (IIIa, IIIb) were continually present bound to chromatin throughout the developmental sequences except the IIb form which was absent at the latest stage. However, a great multiplicity (9 total) of Class II activities (totally inhibited by alpha-amanitin) were observed to be bound to chromatin at the 2nd day stage. These forms were first released from the chromatin complex and recovered in a soluble pool (4th day stage). Subsequent hypocotyl development was accompanied by the gradual disappearance of these Class II subspecies from this pool (6th day) until only two soluble species and one chromatin-bound Class II activity remained (8th day). These observations indicate that the early development of this tissue is accompanied by a dramatic alteration in the conplexity of chromatin-bound RNA polymerase subspecies. Such events may in part determine the domain of RNA secies synthesized at successive developmental stages.