3831121 eccDNA Extrachromosomal circular DNA 216 3831122 eccDNA Endogenous Circular DNA 1 3831123 eccDNA extra-chromosomal circular DNA mechanism 1 3831124 eccDNA extrachromosomal circles of DNA 1 3831120 eccDNA Extrachromosomal circular deoxyribonucleic acid 1