S. Yamashita et al., TAM3 IN ANTIRRHINUM-MAJUS IS EXCEPTIONAL TRANSPOSON IN RESISTANT TO ALTERATION BY ABORTIVE GAP REPAIR - IDENTIFICATION OF NESTED TRANSPOSONS, MGG. Molecular & general genetics, 259(5), 1998, pp. 468-474
Most transposon families consist of heterogeneous copies with varying
sizes. In contrast, the Tam3 copies in Antirrhinum majus are known to
have exceptionally conserved structures of uniform size. Gap repair ha
s been reported to be involved in the structural alteration of copies
from several transposon families. In this study, we have asked whether
or not gap repair has affected Tam3 copies. Five Tam3 copies carrying
aberrant sequences were selected from 40 independent Tam3 clones and
their sequences were analyzed. Two of the five copies contain insertio
ns in the Tam3 sequence. These two insertions, designated Tam356 and T
am661, are typical transposon-like sequences, which have terminal inve
rted repeats and cause target site duplication. These nested transposo
ns were obviously associated with transpositional events, and did not
originate from the gap-repair process. The remaining three copies had
lost large parts of the Tam3 sequence. We could not find any relations
hip between the deletions of Tam3 sequence in the three copies and gap
repair. PCR analysis of a Tam3 excision site in the nivea(recurrence:
Tam3) mutant also showed that most of the repair events after the Tam3
excision involved end-joining. In addition to the results obtained he
re, among the other clones isolated, we could not find any of the inte
rnally deleted copies that comprise a major part of other transposon f
amilies. All of these data suggest that some feature of the Tam3 struc
ture suppresses the structural alterations that are otherwise generate
d during the gap repair process.