Structural conservation of the transposon Tam3 family in Antirrhinum majusand estimation of the number of copies able to transpose

We have investigated the organization of the transposon Tam3 family in Anti rrhinum majus. Genomic hybridization experiments and characterization of 40 independent Tam3 clones isolated from an A. majus plant revealed that the Tam3 family is quite conserved and the copy sizes are uniform. We did not f ind any copy with a deleted internal sequence, unlike what is usually obser ved in other transposons; This exceptionally conserved structure of the Tam 3 family was confirmed by PCR and sequencing analyses. Sequencing analysis identified eight copies with sequences completely identical to that of the Tam3 transposase gene. These results suggested that a considerable number o f autonomous Tam3 copies are present in the genome of A. majus. Among 24 co pies which are surrounded by single copy regions of the genome, 14 copies a re present as specific insertions in the line which we used, but absent in other lines. These copies are therefore predicted to be movable. If this ra tio is the same for all Tam3 copies in a genome, then a maximum of 60% of t he copies are estimated to be movable in the genome. The relatively high fr equency of gene tagged by Tam3 might reflect the large number of movable co pies in the genome.