New AUG initiation codons in a long 5’ UTR create four dominant negative alleles of the Drosophila C₂H₂ zinc-finger gene ovo

Abstract

 Promoters active in the germline produce OVO-A and OVO-B mRNAs encoding isoforms of a putative transcription factor. The isoforms have a common C₂H₂ zinc-finger domain but different N-termini that include potential effector domains. Single point mutations in three dominant-negative ovo ^Dmutations result in new in-frame initiation codons in OVO-B mRNAs and amino acid substitutions within charged regions of OVO-A proteins. Three lines of evidence suggest that the dominant activity is due to the new initiation codons in OVO-B mRNAs and not the amino acid substitutions in OVO-A. First, we made a fourth ovo ^Dallele by inserting a new in-frame AUG. This ovo ^D4allele encodes a nearly full-length OVO-A isoform from OVO-B mRNAs. Second, engineered stop codons in ovo ^D1downstream of the new AUG abolished dominant negative activity. Third, a substantial deletion of an OVO-A region encoding a highly charged amino acid domain fully rescued loss-of-function ovo alleles. These data suggest that ovo ^Dmutations result in inappropriate expression of OVO-A in the female germline.