Abstract
New rudimentary (r) mutants have been isolated following mutagenesis with ethyl methanesulfonate (r(LE)), ICR-170 (r(LI)) and X rays (r(LX)). From wing phenotype measurements on homoallelic females, it has been shown that the r(LE) mutant series includes several leaky alleles, as well as alleles that produce moderate and strong r phenotypes. All of the tested r(LI) alleles yielded strong r phenotypes in homoallelic females, whereas the r(LX) series was found to include both moderate and strong alleles. Based on allele complementation for the wing phenotype, it was found that all three mutant series include both complementing and noncomplementing alleles, but the relative frequencies of these two types of alleles differ considerably among the three series. Complementing alleles comprise most of the r(LE) mutant series (19 of 25) and almost one-half of the r(LX) series (five of 12), while only one of 16 r(LI) mutants is a complementing allele. Data from enzyme assays of mutants mostly support the direct correlation of genetic complementation units with the activities of the first three enzymes in the de novo pyrimidine biosynthetic pathway. All of these findings are discussed in light of evidence that these three enzymes are contained within a trienzyme complex in animals. We conclude that the available genetic evidence supports the contention that the trienzyme complex is encoded by a single mRNA.
