Replication and transcription in the course of DNA amplification of the C3 and C8 DNA puffs of Rhynchosciara americana.

The synchronous development of a sibling group of Rhynchosciara larvae enables us to follow the relationship between the local transcription and extrareplication of C3 and C8 DNA puffs. Although DNA amplification at these two loci takes place during the last cycle of DNA duplication in salivary gland chromosomes, a different timing of puff expression was observed for the two regions analysed. C3 puff transcription is a late event in relation to the C8 counterpart. We present evidence that this might be a consequence of the different firing of DNA amplification in both loci. No signs of DNA rearrangements were detected with probes that extend the previously analysed regions.