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# Mechanism of Suppression in Drosophila: Control of Sepiapterin Synthase at the Purple Locus

John J. Yim, E. H. Grell and K. Bruce Jacobson
Science
New Series, Vol. 198, No. 4322 (Dec. 16, 1977), pp. 1168-1170
Stable URL: http://www.jstor.org/stable/1745705
Page Count: 3
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## Abstract

The amounts of sepiapterin and red pteridine eye pigments (drosopterins) in Drosophila melanogaster are known to be reduced in the purple mutant and restored to normal by a suppressor mutation. We show here that sepiapterin synthase activity is 30 percent of normal in pr and pr$^{\text{bw}}$, two naturally occurring alleles of purple, and is restored to nearly normal levels by the suppressor su(s)$^{2}$. A heterozygote of two newly induced alleles of pr has even lower enzyme activity (< 10 percent). The sepiapterin synthase activity is proportional to the number of wild-type pr alleles in flies when one and two copies of the allele are present and is higher in three-than in two-dose flies. We hypothesize that the purple locus may be a structural gene for sepiapterin synthase in Drosophila.

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