Visualization of nascent transcripts on Drosophila polytene chromosomes using brUTP incorporation

Polytene chromosomes from the salivary gland cells of Drosophila third instar larvae have been used extensively for cytological and genetic studies. Polytene chromosomes have also been used to study transcription because an actively transcribing gene is often manifested as a localized region of chromatin decondensation or "puff". Several methods have been developed to detect sites of active transcription on polytenes. All of these studies led us to investigate whether BrUTP could be used to label nascent transcripts on Drosophila polytene chromosomes.