Terminal redundancy and circular permutation of mycoplasma virus L3 DNA

This communication reports the physical map of mycoplasma virus L3 (MV-L3) DNA derived from restriction patterns obtained by digestion with seven different restriction endonucleases. The length of the restriction map is 36,200 bp in contrast to the contour length of native MV-L3 DNA molecules which is 39,400 bp as determined by electron microscopy. The difference in length of 3,200 bp (corresponding to 8.1% of the native viral DNA contour length) is explained by terminal redundancy. It was possible to clone all fragments from particular restriction patterns into Escherichia coli vector pAT153, an indication of circular permutation within a population of MV-L3 DNA. However clear evidence has been obtained from the molar ratios of fragments and from hybridization experiments. We suppose that viral DNA is packaged from a concatemeric precursor molecule starting at a specific site called pac.