Modifier of rudimentary^p1,mod(r)^p1, a trans-acting regulatory mutation of rudimentary

Abstract

Modifier of rudimentary^p1 (mod(r)^p1) is a hybrid dysgenesis-induced mutation isolated as a suppressor ofr^hd1, a hypomorphicrudimentary(r) allele inDrosophila melanogaster. mod(r)^p1 has opposite effects on two of therudimentary mutant phenotypes. It suppresses the wing truncation associated with hypomorphicr alleles, which was the phenotype used to isolate it. On the other hand, it does not suppress the sterility ofr females and in fact decreases the fertility of wildtype females. This infertility is associated with a drastic decrease inr expression inmod(r)^p1 females. P element-tagging was used to clone the mutant allele,mod(r)^p1. Subsequently, 28 kb of genomic DNA encompassing the wild-typemod(r) gene in the chromosomal region 1B was cloned.mod(r) encodes a 1.3 kb transcript which is not detected in themod(r)^p1 mutant. The sequences ofmod(r) cDNA clones reveal that the gene encodes a protein of 200 amino acids in length. When compared to sequences in GenBank, the amino acid sequence did not reveal any long sequence similarities. However, the structure of the protein reveals similarities to known transcription factors. The N-terminal half of the protein is very acidic, whereas the C-terminal half is basic. The basic domain suggests a possible DNA-binding domain, while the acidic domain suggests a transcriptional activation domain. Consistent with this possibility is the fact thatmod(r) acts through the 5′ control region of therudimentary gene to control its expression.