Isolation and partial characterization of 2-microns yeast plasmid as a transcriptionally active minichromosome.

Yeast cell extracts from 2-microns-containing strains (cir+) showed higher transcriptional activity than their corresponding isogenic sets (cir0). These extracts were used to purify transcriptionally active 2-microns minichromosomes in a sucrose gradient. Minichromosomes were transcribed in vitro and, employing hybridization techniques, the RNA synthesized was shown to present 2-microns-specific sequences. This model system should permit the direct study of transcriptionally active eucaryotic chromatin.