UNUSUAL DNA FORMS IN THE DARC146 SEQUENCE

The DARC146 fragment enabling autonomous replication of bacterial vect ors in mammalian cells was earlier identified in the complex form of D NA polymerase a, and cloned; its sequencing revealed an inverted repea t admitting a hairpin (cruciform) conformation. In this work, syntheti c oligonucleotides reproducing this inverted repeat were shown to exis t in vitro in three forms: linear, self-complementary duplex, and cruc iform. Trimethylpsoralen fixation demonstrated that the cruciform in D ARC146 introduced into a bacterial plasmid is preserved in vivo.