Isolation of single stranded transcription sites from human nuclear DNA.

Single stranded DNA (ss-DNA) isolated from nuclear DNA of human rhabdomyosarcoma (RD line) cells amounts to 2% of total DNA. As compared with native double-stranded DNA (ds-DNA), ss-DNA has a lower mean sedimentation coefficient, higher buoyant density, contains fewer repeated DNA sequences and a greater proportion of it can be hybridized to human RNAs (up to 35% and less than 8% for ds-DNA). The hybridization kinetics determined by S1 nuclease digestion and verified by other methods (hydroxylapatite chromatography, density gradient centrifugation and thermal melting) indicate that ss-DNA corresponds to a great number and variety of transcripts. These data are discussed as evidence for DNA strand dissociation in the course of gene activity.