This is the double-stranded, covalently closed, circular form of ΦX174 RF I DNA (supercoiled).

The molecular weight of ΦX174 RF I is 3.50 x 10^6 daltons and it is 5,386 base pairs in length. The vast majority of the molecules are RF I, and the remainder are RF II, as determined by agarose gel electrophoresis. DNASU and Addgene are central repositories for plasmid clones and collections that may also be helpful. The ΦX174 RF I DNA is isolated from E. coli HF 4704 infected with ΦX174 am3 cs70 by a modification of the method of Godson and Vapnek (nucleotide sequenced by F. Sanger).