Genes from two intermoult puffs in Drosophila virilis polytene chromosomes are differentially transcribed during larval development.

Genes from two Drosophila virilis intermoult puffs were isolated by microcloning. From puff 16A on the X-chromosome a 2.9 kb DNA fragment was obtained, which hybridizes with three transcripts. Two of them represent the mRNAs for larval glue proteins. They are found in different abundancies in third larval instar salivary glands, but also in minor amounts in midgut and in fat body. In puff 55E on chromosome III two genes were identified. They are transcribed exclusively in salivary glands during all three larval instars. Therefore, their products must be related to another gland-specific function, which is sustained throughout larval life.