Chromosome puff activity and protein synthesis in larval salivary glands of Drosophila melanogaster.

Secretion proteins from larval salivary glands of Drosophila melanogaster were analyzed with acrylamide gel electrophoresis. Four fractions were found; three showed electrophoretic variants in different wild-type stocks. Crossbreeding and cytogenetic techniques were used to localize the genes responsible for the two main fractions: The gene for fraction 3 was found to lie within a segment of the third chromosome which includes section 68C; the gene for fraction 4, Sgs-4, was found to lie within section 3C8-3D1 of the X chromosome (1 - 3-5). The puffs within these sections of the giant chromosomes are active before and during secretion synthesis and become inactive as secretion synthesis ceases. Larvae of one wild-type stock which lack protein fraction 4 do not exhibit any puffing in 3C. The relative amount of protein 4 in the salivary secretion shows a marked dependence on the dosage of the Sgs-4 gene in both duplication and deficiency genotypes. The active site within puff 3C11-12 apparently contains the structural gene for protein 4.