The Ds element in the Adh1-2F11::Ds2 allele of Zea mays has been cloned and sequenced. The element, designated Ds2, belongs to a family of 10-12 similar or identical elements in the maize genome. It is identical to the Ds insertion in the Bz2-m allele (see report by K. Theres and P. Starlinger, this volume). Ds2 contains two segments at its termini that are nearly identical to Ac. These are approximately 550 and 300 bp, respectively. Adjacent to the left homologous part, there is a segment formed by duplications and triplications of Ac sequence. It is followed by a segment of approximately 200 bp length that is unrelated to ac. Another sequence segment found both in Ac and Ds2 seems to be derived from a common progenitor sequence. The first step in the evolution of this progenitor sequence was the duplication of 43 bp. Each of these sequences was further altered by the addition of small sequence duplications, which could be transposon footprints, and a few other insertions and deletions. By comparing the duplicated sequences both in Ac and in Ds2, it is seen that the original sequence is altered to a larger extent in Ac than in Ds2. These complicated events show that both Ac and its derivative Ds elements are in a process of rapid evolution.
Cleaving genomic DNA with restriction enzymes that cut inside the termini of Ds2, most of the Ds2-related sequences are found in one band of the size expected from cleaving cloned Ds2. Slightly deviating bands are found, however, indicating that Ds2 itself is still evolving. The copy number of Ds2-related sequences varies between 6 and 12 copies in different maize lines investigated.
Armin Merckelbach and Peter Starlinger
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