Fig. 1. Mutations and structure of the retn gene. The structure of the retn gene is shown (introns not to scale), including the previously undetected exon 1-4 and exon 1-6 splice variants. Positions and structures derived from Gregory et al. (Gregory et al., 1996) and from our analysis of the genomic sequence of the region. The regions shown in white encode the extended ARID box DNA-binding domain. The viable ('retn class') alleles retn^RO44, retn^z2-428 and retn^RU50 encode missense mutations within the ARID box. Embryonic lethal ('dri class') alleles retn^dri1 and retn^driB142 encode nonsense mutations. P-element insertions retn^dri7 and retn^dri8 map in or near retn exon 1. retn-Gal4 insertions were created by targeted transposition into the retn^dri7 and retn^dri8 positions (Shandala et al., 1999).