Organization of the Tgm family of transposable elements in soybean

Abstract

We have compared the organization of six Tgm elements that were selected from a genomic library of soybean DNA on the basis of hybridization with subcloned regions of Tgm 1 (transposon, Glycine max) from the seed lectin gene. These elements ranged in size from 1.6 kbp to greater than 12 kbp. Tgm2, Tgm3, Tgm4 and Tgm5 represent partial isolates in which the genomic clone contained a 3' but not a 5' terminus of the element; while Tgm6 and Tgm7, like Tgm1, were small isolates flanked by both 5' and 3' nonelement sequences. Cross-hybridization studies between subcloned portions of these seven elements identified regions of homology which suggest that the Tgm transposable elements of soybean form a family of deletion derivatives. In addition to internal deletion events, numerous deletions and base substitutions are also present within the borders of these elements which are comprised of the same tandemly repeated sequence. The 39% amino acid homology between a 1 kb portion of an open reading frame in Tgm4 and Tgm5 and ORF1, an open frame from the first intron of the maize Enhancer (Suppressor-mutator) transposable element, suggests that both elements encode a common function that requires a high degree of protein conservation.