Mapping of inverted repeated DNA sequences within the genome of simian virus 40

Single-stranded, linear DNA of simian virus 40 (SV40) created by denaturing the endonuclease EcoRI- or Hpa II-generated, linear, double-stranded products from form I DNA of SV40 was analyzed for regions of inverted repeated sequences by visualization with the electron microscope. Six hairpin loops were found at positions 0.11-0.30 (two loops forming a "rabbit ears" structure), 0.47-0.52, 0.63-0.68, 0.70-0.76, and 0.90-0.96. The nucleotide sequences within all of these inverted repeats may be related since the looped regions can crosshybridize with one another and, thus, the SV40 genome may contain regions of interspersed repeated and unique sequences. The map positions of the 3' and 5' ends of the early and late messenger RNAs, as determined by others, lie within regions of inverted repeated sequences. Previously recorded recombination events that occurred either within the SV40 genome or between SV40 DNA and other genomes have apparently occurred frequently at positions of inverted repeated sequences within the SV40 DNA.