Maize lines known as Robertson’s Mutator (Mu) lines generate unstable recessive mutations at high rates. These lines carry actively transposing copies of the elements Mu1 and Mu1.7. We have discovered extrachromosomal forms of the Mu1 and Mu1.7 transposons. We have shown that these molecules are most likely covalently closed circular DNA (ccDNA). Further, we find that their occurrence is correlated with Mu transposition so that they are probably generated during Mu transposition as transposition intermediates, abortive intermediates, or excision products. Our data suggest that Mu1 and Mu1.7 circles account for a significant fraction of the total ccDNA found in Mutator lines, but that other Mu-homologous circles are also present in these lines.
KeywordsMaize Line Barley Stripe Mosaic Virus Tn10 Transposase Excision Product Circular Fraction
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