The Teo1 insert from Zea mexicana teosinte Guerrero is a composite of the Cin2 and Cin3 elements

The 3 kb Teo1 DNA insert has been described recently in CGNL 57:159. Further analysis revealed that it is a composite structure consisting of a Cin2 and a Cin3 element. The Cin2 element is 1.2 kb long, contains about 140 bp direct repeats at its ends and is flanked by a 3 bp duplication probably generated during the integration process, as usually observed with transposable elements. Into this element the Cin3 element has integrated. This second element is 1.8 kb in length and has 634 bp inverted repeats flanked by a 9 bp duplication. This composite structure, previously called Teo1, was found in teosinte Guerrero by its homology to a unique 5 kb fragment, LCI of Zea mays Line C. DNA sequence comparison between LCl and the Teo1-containing clone TG2 revealed that LCI still contains one of the direct repeats of Cin2 flanked by the same 3 bp duplication found to border the composite Teo1 structure. Hence we think that LCl or an equivalent clone isolated from teosinte is a recombinational derivative of Teo1.

Using Cin2 and Cin3 as specific probes in Southern hybridization experiments with genomic DNAs of various maize and teosinte lines, both elements were found to be repetitive in these lines. Cin2 seems to be less repetitive than Cin3. Cloning experiments revealed that CM2 and Cin3 usually occur as individual elements in the maize and teosinte genome. For example, a 6.2 kb DNA clone from the Zea mays line Hickory King contains only the Cin2 element in an LCI-homologous segment.

The Cin2 structure resembles copia-elements of Drosophila and also Ty elements of yeast. As in these systems solo copies of the LTR-like direct repeats are found. Cin3 has a similar structure to that of Robertson's Mutator. Both are flanked by a 9bp duplication, but the Mu-1 element has shorter inverted repeats (215 bp). The integration of one element into a different element has been described already in other organisms including Drosophila and some prokaryotes. Such composite structures have not been described in plants until now.

Jutta Blumberg vel Spalve, Nancy S. Shepherd and Heinz Saedler

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