Search

Tadis an active LINE-like retrotransposon isolated from the Adiopodoumé strain of Neurospora crassa.Extensive analysis of other Neurospora strains has revealed no other strain with active Tad,but all strains tested have multiple copies of defective Tadelements. We have examined the ability of Tadto survive during the sexual cycle of Neurospora and find that active Tadis rapidly eliminated. The characteristics of this elimination suggest that the repeat-induced point mutation (RIP) mechanism was responsible. By the use of transformation to switch the mating type of the Adiopodoumé strain we concluded that this strain is not defective in the RIP process. Analysis of defective Tadelements isolated from a variety of strains indicates that the major difference between these elements and active Tadis due to the presence of a large number of G-C to A-T transition mutations. This would be expected if the changes were due primarily to the RIP process. Mapping of a selection of defective Tadelements reveals that they are present on all of the chromosomes; however, many of the elements are not widely shared among strains. This suggests that repeated introduction and elimination of Tadelements has occurred. Mechanisms that might be responsible for this repeated introduction are discussed.