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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