Transposition of Ac in Tobacco
The maize transposable element Activator (Ac) was first identified and studied genetically by Barbara McClintock (15; for review, see Ref. 9). The Ac element is capable of transposing autonomously, and it can also trans-activate the transposition of a group of elements collectively designated Dissociation (Ds) elements. Ac and Ds elements comprise a maize transposon family. Many elements of this family have been cloned and subjected to structural analysis (3,6,10). The Ac element is a small, 4.6-kilobase (kb) transposon that has an 11-base-pair (bp) terminal inverted repetition and generates an 8-bp duplication upon insertion. Sequence analysis of the element has revealed the presence of three major open reading frames (ORFs) (16,19). Recently, an RNA transcript of 3.5 kb was identified and found exclusively in maize lines that carried an active Ac (13). Overlapping cDNA clones spanning most of the mRNA were sequenced. The transcript contains a 600–700 nucleotide long untranslated leader, an open reading frame encoding 807 amino acids, and an untranslated 3′ sequence of 239 nucleotides. Four introns with a combined length of 654 bases are removed from the primary transcript.
KeywordsCallus Line Restriction Enzyme Fragment Major Open Reading Frame BamHI Restriction Enzyme Site Progenitor Plant
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