Thymidylate synthetase in mutants of Drosophila melanogaster.

Thymidylate synthetase has been examined with respect to the normal pattern of activity throughout the development of the Oregon-R strain of Drosophila melanogaster. Large amounts of the enzyme are present in both the unfertilized and the fertilized eggs. A comparison of the ovarian thymidylate synthetase activity of the Oregon-R strain and the female sterility mutants, fs(2)B, fu, and fs(1)N, indicates variations in the activity of this enzyme in each strain. At four days of age, the ovarian-specific activity of the female sterility mutants is comparable to or less than that of the Oregon-R strain, but it is reduced at fifteen days of age. The enzyme activity per ovary is low in the fs(2)B strain but is similar in the Oregon-R, fu, and fs(1)N strains. When expressed as activity per organism, thymidylate synthetase declines after six to eight hours of development until the minimal level is reached in the late embryonic stage. Enzyme activity rises throughout the larval instars, reaching a maximum immediately after puparium formation. The activity decreases during pupation, but rises again during the first four days of adult life.