STRUCTURAL-ANALYSIS OF TPN1, A TRANSPOSABLE ELEMENT ISOLATED FROM JAPANESE MORNING GLORY BEARING VARIEGATED FLOWERS

The 6.4 kb transposable element Tpn 1 belonging to the En/Spm family w as found within one of the DFR (dihydroflavonol-4-reductase) genes for anthocyanin biosynthesis in a line of Japanese morning glory (Pharbit is nil) bearing variegated flowers. Sequencing of the Tpn 1 element re vealed that it is 6412 bp long and carries 28-bp perfect terminal inve rted repeats. Its subterminal repetitive regions, believed to be the c is-acting sequences for transposition, show striking structural featur es. Twenty-two copies of the 10-bp sequence motif GACAACGGTT can be fo und as direct or inverted repeats within 650 bp of the 5' end of the e lement, and 33 copies of the sequence motif lie within 800 bp of the 3 ' terminus. All these 22 copies of the sequence motif near the 5' term inus and 30 copies in the 3' terminal region are arranged as inverted repeats and 3-8 bp AT-rich sequences are detected between these invert ed repeats. In addition, four copies of 122-bp tandem repeats and six copies of 104-bp tandem repeats are present in the 5' and 3' subtermin al repetitive regions, respectively. No large open reading frame chara cteristic of autonomous elements of the En/Spm family can be detected within the element. The results are discussed with respect to heritabl e changes in flower variegation in this line of Japanese morning glory .