Isolation of two new CACTA transposable elements from anthocyanin genes in maize
--Techen, N, Borchert, L, Scheffler, BE, Wienand, U

Transposable element (TE) specific features are terminal inverted repeats and a target site duplication upon integration. Elements containing identical inverted repeats have been grouped into families. The En/Spm element from maize (Pereira, A, H Cuypers, A Gierl, Z Schwartz-Sommer, H Saedler. 1986. EMBO J. 5:835-841; Masson, P, R. Surosky, JA Kingsbury, N Federoff, 1987. Genetics 177:117-137) belongs to the so called CACTA family of elements. The characteristics of the CACTA family, which have been described from different species, is the CACTA terminal inverted repeat and a 3 bp target site duplication upon integration. Other elements of this family are Tam1 from Antirrhinum majus (Nacken, WKF, R Piotrawiak, H Saedler, H. Sommer. 1991. Mol. Gen Genet. 228:201-208), Tgm1 from soybean (Rhodes, PR, LO Vodkin. 1985. Proc. Natl. Acad. Sci. USA 82:493-497), and Pis1 from pea (Shirsa, AH. 1988. Mol. Gen. Genet. 212:129-133). We have found two further such elements in maize through the molecular analysis of anthocyanin genes. These new CACTA elements have been identified through the analysis of the In (Intensifier) gene and the C2 (Chalcone synthase) mutant C2-Idf (Inhibitor diffuse). In Intron 6 of In a 948 bp long CACTA element and a 3 bp target site duplication have been identified by comparing the sequences of the alleles In and In-D (Intensifier dilute). The highly repetitive element contains several direct and indirect repeats, and palindromic sequences. The analysis of this transposable element showed a region of 450 bp with a high AT content (69%). Polyadenylated homologous transcripts of this element have been found in young seedlings, roots, embryos and tassels. Six such transcripts were isolated from a cDNA library and sequenced. The sequences are highly conserved (78-88%) and vary between 109 bp and 153 bp in length. Part of the CACTA element (about 500 bp) is also inserted in the C2, Whp, and C1 genes. Insignificant homology was detected when compared to the ILS-1 TE (Alrefai, R, B Orozco, T Rocheford. 1994. Plant Physiol 106:803-804). So far, no regulatory function of this element could be detected. Upon sequence analysis of the C2-Idf allele another member of the CACTA element family was discovered. It is integrated into the promoter of one of the three known "C2 copies" present in the mutant C2-Idf. This element is 1165 bp in length.

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