MINOR-MYOSIN, A NOVEL MYOSIN ISOFORM SYNTHESIZED PREFERENTIALLY IN DROSOPHILA TESTIS IS ENCODED BY THE MUSCLE MYOSIN HEAVY-CHAIN GENE

Searching for structural proteins involved in spermatogenesis of Drosophila, we found a novel myosin isoform in the testis of Drosophila hydei and D. melanogaster. The transcript encoding this isoform, which we called 'minor-myosin', initiates within the intron between exons 12 and 13 of the muscle myosin heavy chain (mMHC) gene. Minor-myosin contains a common myosin tail but no ordinary myosin head domain. Instead, it has a short N-terminal domain which displays similarity with the N-termini of certain myosin light chain proteins. Western blots with male germ line mutants showed that the novel mMHC isoform is synthesized in the male germ cells, mainly postmeiotically. However, minor-myosin is not testis-specific, as it is expressed at a low level in the fly carcasses. The possible functions of the myosin isoform in the male germ line are discussed.