Organization of contractile protein genes within the 88F subdivision of the D. melanogaster third chromosome.

We have investigated contractile protein gene arrangement within the 88F subdivision of the Drosophila melanogaster third chromosome. We show that at least five antigenically related myofibrillar proteins, three of which accumulate only within indirect flight muscles, are encoded by a 20 kilobase chromosome segment located 140 kilobases proximal to the act88F actin gene. The chromosome segment includes two transcribed regions, each of which directs the synthesis of multiple mRNAs. RNA blot-hybridization experiments and DNA sequencing suggest that overlapping transcripts are generated by differential RNA splicing. The nucleotide sequence also establishes that two of the encoded proteins are tropomyosin isoforms, and two are related to tropomyosin. The arrangement of myofibrillar genes parallels the distribution of third chromosome mutations that disrupt indirect flight muscle formation.