Loop structures in hybrids of early RNA and the separated strands of adenovirus DNA

Separated strands of adenovirus DNA were annealed with early cytoplasmic RNA and visualized in the electron microscope. DNA-RNA duplex regions within the DNA filaments could be recognized by their heavy contour. This contour was often interrupted at distinct locations by loops of displaced, single-stranded DNA. Loops have been observed and mapped in all four early regions of the genome. The structures appear to signal hitherto unknown mechanisms of eukaryotic gene expression.