Transcriptionally active SV40 minichromosomes are restriction enzyme sensitive and contain a nucleosome-free origin region

Abstract

A nucleosoroe-free region or gap containing the origin of replication and the transcriptional promoter elenents is observed on 20 to 25% of the SV40 mini chromosomes Isolated at physiological 1on1c strength late In Infection. We used the preferential sensitivity of the gapped minichromosomes to restriction enzymes to obtain sucrose gradient fractions containing 50 to 80% of gapped molecules. The same fractions are also enriched 1n RNA polymerase B (II) molecules engaged 1n transcription. Using electron microscopy, we demonstrate here that the transcriptional complexes are preferentially sensitive to restriction enzyme digestion, which Indicate that they represent a subpopulation of the gapped minichromosomes. © 1986 IRL Press Limited.