Gene amplification in Rhynchosciara salivary gland chromosomes.

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Abstract
Late in the 4th larval instar, several regions of the R. americana salivary gland chromosomes undergo DNA puffing. A library of cloned c[complementary]DNA was synthesized from poly(A)+RNA, which was isolated from salivary glands during the period of development when the DNA puffs were active. Clones representative of 3 genes active during this period, but not active at earlier developmental periods of the gland, were studied. One of these genes is not amplified during the developmental process and encodes a 0.6-kilobase RNA molecule. The other 2 genes are located within the DNA-puff sites C3 and C8 and encode 1.25-kilobase and 1.95-kilobase RNA molecules, respectively. Each of these genes probably undergoes 16-fold amplification during DNA puffing.