TRANSNUCLEAR RETROTRANSPOSITION OF THE TAD ELEMENT OF NEUROSPORA

Tad is a LINE-like DNA element found in Neurospora crassa. A Neurospora artificial intron based on the first intron of the am (glutamate dehydrogenase) gene was constructed and introduced, in the correct orientation, into a unique Nru I site in open reading frame 1 of an active Tad element, Tad1-1. Transformants containing the Tad element with the artificial intron were placed in forced heterokaryons with strains lacking Tad elements. Tad was shown to transpose between nuclei in these heterokaryons. Examination of the transposed Tad elements showed that the intron had been precisely removed in all cases. This confirms that Tad is a retrotransposon and that there is a cytoplasmic phase in these retrotransposition events.