The role of subterminal sites of transposable element Ds of Zea mays in excision

Abstract

Transposition depends on DNA sequences located at or near the termini of the transposon. In the maize transposable element Ds, these sequences were studied by site-directed mutagenesis followed by a transient excision assay in Petunia protoplasts. The transposase-binding AAACGG motifs found in large numbers in the element are important, but none of them is in itself indispensable, for excision. However, mutation of an isolated motif at the 3' end considerably reduced excisability. The inverted termini were confirmed to be indispensable. Point mutations in regions outside the inverted termini of Ds and not located in the transposase-binding motifs had, in some cases, a pronounced effect on excision frequency. The implications of these findings are discussed.

Functional Dissection of the Tol2 Transposable Element Identified the Minimal cis-Sequence and a Highly Repetitive Sequence in the Subterminal Region Essential for Transposition

“…In the case of Ac, 238 bp from the 59-end and 209 bp from the 39-end, containing 11-bp TIRs and the subterminal regions, are required for the excision activity (Coupland et al 1989). The TIRs of Ac are also essential for excision (Chatterjee and Starlinger 1995). The Ac transposase binds to a 6-bp sequence, AAACGG (Kunze and Starlinger 1989), and the 59 and 39 subterminal sequences contain 10 and 3 copies of this motif, respectively (Chatterjee and Starlinger 1995).…”

“…The TIRs of Ac are also essential for excision (Chatterjee and Starlinger 1995). The Ac transposase binds to a 6-bp sequence, AAACGG (Kunze and Starlinger 1989), and the 59 and 39 subterminal sequences contain 10 and 3 copies of this motif, respectively (Chatterjee and Starlinger 1995). While mutations in these motifs reduce the excision activity, none of them by itself is indispensable and only combinations of mutations in more than six motifs abolish the excision activity nearly completely (Chatterjee and Starlinger 1995).…”

“…In the case of Ac from maize, 238 bp from the 59-end and 209 bp from the 39-end are sufficient and required for transposition (Coupland et al 1989). These subterminal sequences contain 13 AAACGG sequences (Chatterjee and Starlinger 1995), which are the binding motif for the Ac transposase (Kunze and Starlinger 1989). While mutations in some of these motifs reduced or abolished the cis-activity required for excision (Chatterjee and Starlinger 1995), some binding motifs were dispensable, and roles of these sequences in transposition have not been elucidated (Chatterjee and Starlinger 1995).…”

“…These subterminal sequences contain 13 AAACGG sequences (Chatterjee and Starlinger 1995), which are the binding motif for the Ac transposase (Kunze and Starlinger 1989). While mutations in some of these motifs reduced or abolished the cis-activity required for excision (Chatterjee and Starlinger 1995), some binding motifs were dispensable, and roles of these sequences in transposition have not been elucidated (Chatterjee and Starlinger 1995). In the case of Tag1 from Arabidopsis, 98 bp from the 59-end and 109 bp from the 39 end are sufficient for transposition.…”

Transposase binding site methylation in the epigenetically inactivated Ac derivative Ds‐cy

“…Between residues 105 and 152 a prominent group of seven binding sites with opposite orientation is found. The integrity of these sites appears to be less critical for transposition as point mutations of individual sites within this cluster, and even the destruction of the prominent binding site quartet between positions 130-152 results in only a minor reduction in transposition frequency (Chatterjee and Starlinger, 1995). Of the seven most internally located TPase binding sites (residues 165-235), five point into the same direction as the terminal group.…”