Precise and imprecise somatic excision of the transposon Tcl in the nematodeC.elegans

Abstract

Eleven chromosomal products of somatic excision of Tcl transposable elements have been cloned and sequenced. The cloning method did not involve genetic reversion; therefore the products analyzed should be representative. Six empty religated target sites were from excision of one Tcl element inserted near actin genes on linkage group V; five were from a second Tcl element inserted elsewhere on the same linkage group. All six products from the first element were identical in sequence to an empty target site from a second strain, indicating excision had been precise. Two of the products from the second element were also precise, whereas the other three contained four extra nucleotides at the point of excision, indicating an imprecise excision. The four nucleotides are the same in all cases and could represent two terminal nucleotides of the transposon plus a two-nucleotide target site duplication. The difference in the ratio of precise to imprecise excision at the two insertion sites suggests a possible chromosomal position effect on the pathway of Tcl somatic excision.