Isolation of a transposable element from Neurospora crassa

A Neurospora crassa strain from Adiopodoumé, Ivory Coast, contains multiple copies of a transposable element, Tad. The element was detected as a 7-kilobase insertion in two independently isolated spontaneous forward mutants of the am (glutamate dehydrogenase) gene. Laboratory strains do not contain Tad. All progeny from crosses of the Adiopodoumé strain to laboratory strains contain multiple copies. When the element was inserted in am, target sequences of 14 and 17 base pairs were duplicated in the two cases analyzed. One mutation, caused by the insertion of Tad at the beginning of the am coding sequence, is genetically stable. The other mutation, caused by insertion upstream of the transcriptional start site, has a reversion frequency of 2.5 x 10(-3). Precise excisions of Tad have not been found.