Cyclin proteins are one of the important components of the mechanism regulating mitosis in eukaryotic cells. We isolated a Drosophila Cyclin-A mutant in which the progenitor cells of the peripheral nervous system (the sensory mother cells) do not divide properly, causing the loss and other abnormalities of mechanosensory organs in the adult fly. Sequence analysis of the mutant genome reveals that a P element is inserted into the first intron of the Cyclin-A gene. A 13 kb wild-type genomic DNA containing the Cyclin-A transcription units rescued the mutant phenotype when introduced into the mutant fly. The regulation of cell type specific expression of the Cyclin-A gene is discussed.
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