The nucleotide sequence of the autonomous transposable element En-1 isolated from the wx-844::En-1 allele has been determined. En-1 is 8287 bp long. The structure of the mosaic gene 1, coding for the major En transcript, has been established. The promoter of gene 1 is located in the highly structured left end of the element and the gene spans almost the entire length of En-1. The first intron of gene 1 is 4434 nucleotides long and contains two large open reading frames, 2714 bp and 761 bp in size, which hybridize to minor RNA species in Northern blot experiments.