Circular DNAs and RNAs do not have 5' or 3' ends and are therefore very resistant to exonuclease-mediated degradation and are more stable than their linear counterparts.
Circular ssDNA is very stable and highly resistant to exonuclease degradation. This is illustrated in Lane #3 and #5 of a PAGE gel.
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The treatment of linear and circular single stranded DNA with exonuclease I shows that circular single stranded DNA is very stable to degradation by exonucleases.
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