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