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 Droso phila, we found a novel myosin isoform in the testis of Drosophila hyd ei and D. melanogaster. The transcript encoding this isoform, which we called 'minor-myosin', initiates within the intron between exons 12 a nd 13 of the muscle myosin heavy chain (mMHC) gene. Minor-myosin conta ins 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 mal e 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 c arcasses. The possible functions of the myosin isoform in the male ger m line are discussed.