Insertion of 683bp P element in the 1kb EcoRI fragment at the 5' end of the gene, near the transcription start site, and in the same transcriptional orientation as otu.

P element inserted between 8 and 9bp upstream of the first major transcription start site, designated as +1 in Comer et al., Gene 118: 171-179. The target sequence of GGCGCGAT (-1 to -8) is found at both ends of the insertion. Southern analysis revealed the otu²⁰ P insert to be 0.6kb and in the same transcriptional orientation as the otu gene.