Abstract: Drosophila is an excellent model to study spontaneous mutation due to the availability of a large collection of spontaneous mutants, such as body pigment mutants. Previously, we found a spontaneous pigmentation mutant, bsr (black strip), which was confirmed as an allele of ebony (e) and we named it as e^bsr. Subsequent sequencing of genomic DNA revealed a deletion of 953 nucleotides at the 5′end of e^bsr including 206 nucleotides of exon 1 and flanking 747 nucleotides of intron 1. Reverse-transcriptase PCR (RT-PCR) showed that the deletion at the 5′end of e^bsr leads to defective splicing, resulting in a transcriptional product with an additional 3.2 kb upstream of initiation codon AUG. RNA secondary structure analysis indicated that the unspliced 5′UTR folds into complex structure containing several more stem-loops than that of wild-type e. Western blotting results indicated that translation of e was totally suppressed in e^bsr. This favors a model that the change of 5′UTR structure of mRNA prevents the protein translation.

Key words: Drosophila melanogaster, black strip (bsr) mutant, ebony (e), deletion mutation, 5′untranslated region (5′UTR)