Transcription of polyoma virus DNA after interaction with nuclear proteins in vitro

RNA polymerase B, histones and non-histone chromosomal proteins (NHP) extracted from calf thymus nuclei were used for transcription experiments with superhelical form 1 and linear Eco R1 cleaved Polyoma virus DNA. NHP added to DNA with a NHP/DNA weight ratio of 0.5/1 partially inhibited transcription of superhelical DNA but did not affect transcription of linear DNA. The preferential inhibition of form I DNA transcription could be explained by a higher affinity of NHP for this form of DNA: NHP added in excess increased the sedimentation coefficient of superhelical but not of linear DNA. Histones completely inhibited transcription of superhelical DNA, while the only partially inhibited transcription of linear DNA at a histone/DNA ratio of 0.6/1. At the same histones/DNA rato a modification of the sedimentation properties of linear, but not of superhelical DNA was observed. © 1976 Academic Press, Inc.