The activity of two heat shock loci of Drosophila hydei in tissue culture cells and salivary gland cells as analyzed by in situ hybridization of complementary DNA.

Complementary DNA was made to poly A+ nuclear or polysomal RNA isolated from heat shock tissue culture cells of Drosophila hydei. A number of loci other than the four major heat shock loci are labelled after in situ hybridization of these cDNA preparations, while solution hybridization indicated that only about 10% of the cDNA was specific for heat shocked cells. Removal of the fraction of cDNA which could react with 25 degrees C RNA and subsequent in situ hybridization of heat shock specific cDNA indicated that locus 4-81 B, a major salivary gland heat shock locus, is also active at 25 degrees C in tissue culture cells, while locus 4-85 B is specifically activated by heat shock in tissue culture cells. This latter locus is not seen to be clearly puffed in salivary glands, but was shown to be active in that tissue both by direct autoradiography of salivary gland chromosomes after 3H-uridine labeling and by hybridization of cDNA to chromosomal RNA.