Abstract
We have shown that the vestigial (vg) mutant of D. melanogaster has a perturbed nucleotide metabolism compared to various wild-type strains. The mutant is particularly spontaneously resistant to aminopterin. The resistance seems to correlate with an increase in dihydrofolate reductase (DHFR) activity and quantity. The DHRF is a target enzyme of aminopterin. Our results suggest that the vg+ gene could be a regulatory gene acting on the DHFR gene. The wing mutant phenotype being due to a decrease in the thymidylate pool (dTMP) (Silber et al., 1989). In order to understand better the action of the mutant gene on nucleotide metabolism, we have induced suppressor genes of the mutant phenotype by mutagenesis with ethyl methanesulfonate (EMS) and bromouridine (BUR). The suppressor strains obtained display a phenotype intermediate between wild-type and vg phenotype. The action of three independent suppressor genes on eight parameters of nucleotide metabolism is reported here [three enzyme activities, resistance to aminopterin and to fluorodeoxyuridine (FUdR), auxotrophy test and the ability to use exogenous thymidine and uridine]. In comparison to the original vg strain, major changes for the parameters tested are observed. The most striking effects are obtained with the vgBUR27 strain, which is highly sensitive to aminopterin and to fluorodeoxyuridine and didplas the highest thymidine kinase (TK) and DHFR activities within the strains tested. The potential actions of suppressor genes on the vg mutant are discussed.
