Functional dissection of the cis-acting sequences of the arabidopsis transposable element Tag1 reveals dissimilar subterminal sequence and minimal spacing requirements for transposition

The Arabidopsis transposon Tag1 has an unusual subterminal structure contai ning four sets of dissimilar repeats: one set near the 5' end and three nea r the 3' end. To determine sequence requirements for efficient and regulate d transposition, deletion derivatives of Tag1 were tested in;Arabidopsis pl ants. These tests showed that a 98-bp 5' fragment containing the 22-bp inve rted repeat and four copies of the AAACCX (X = C, X, G) 5' subterminal repe at is sufficient for transposition while a 52-bp 5' fragment containing onl y one copy of the subterminal repeat is not. At the 3' end, a 109-bp fragme nt containing four copies of the most 3' repeat TGACCC, but not a 55-bp fra gment, which has no copies of the subterminal repeats, is sufficient for tr ansposition. The 5' and 3' end fragments are not functionally interchangeab le and require an internal spacer DNA of minimal length between 238 and 325 bp to be active. Elements with these minimal requirements show transpositi on rates and developmental control of excision that are comparable to the a utonomous Tag1 element. Last, a DNA-binding activity that interacts with th e 3' 109-bp fragment but not the 5' 98-bp fragment of Tag1 was found in nuc lear extracts of Arabidopsis plants devoid of Tag1.