Intrastrand base pairing in single-stranded deoxyribonucleic acid from ColE1-derived plasmid pCR1

Single strands of EcoRI-cleaved pCR1 deoxyribonucleic acid were examined by electron microscopy for intrastrand base pairing by using partial denaturing conditions. The locations of three stem and loop structures were mapped relative to the inverted repeat of Tn903. Potential roles and origins of these loops are discussed.