Molecular biology of spiroplasma plasmids.

With one exception, all spiroplasma strains examined contained extrachromosomal DNA, most of which was in the form of covalently closed circular plasmids. One plasmid, pIJ2000, carried by Spiroplasma citri strain ASP-1, was purified and characterized and used to probe for related plasmids in other strains. Unsuccessful attempts were made to clone pIJ2000 into Escherichia coli using the vectors pAT153 and pBR322. However, spiroplasma chromosomal DNA fragments could be cloned without difficulty.