Genetic organization of the ci-M-pan region on chromosome IV in Drosophilamelanogaster

The genes cubitus interruptus (ci), ribosomal protein S3A (RpS3A), and pang olin (pan) are localized within 73 kb in the cytological region 101F-102A o n chromosome IV in Drosophila melanogaster. A region of 13 kb harbours the regulatory regions of both ci and pan, transcribed in opposite directions, and a 1.1-kb gene encoding RpS3A. This dense clustering gives rise to very complicated complementation patterns between different alleles in these loc i. We investigated this region genetically and molecularly by use of an enh ancer trap line (IA5), where the P-element was found to be inserted into th e first intron of pan. Screens for imprecise excisions of the P-element wer e performed, and complementations between new and old established mutant li nes were investigated. We found that when mutated or deleted the RpS3A gene gives rise to a Minute phenotype, and we conclude that M(4)101 encodes the ribosomal protein S3A.