Male seminal protein which triggers short- and long-term post-mating behavioral responses (PMR) in female Drosophila (PubMed:3135120, PubMed:19249273, PubMed:20308537, PubMed:19793753, PubMed:15694303, PubMed:24089336). Binds initially to sperm where it is later cleaved to release an active peptide within the female reproductive tract. Signals via the sex peptide receptor (SPR) in female flies; may also act via other receptors (PubMed:20458515, PubMed:20308537, PubMed:24089336). Moderates the activity of distinct neuronal circuitries in the female genital tract to promote specific PMRs including: enhanced ovulation, increased egg laying rate, increased feeding/foraging rate, induced antimicrobial peptide synthesis, reduced mating receptivity, reduced day-time sleep and reduced lifespan in multiple mated females (PubMed:3135120, PubMed:15694303, PubMed:19249273, PubMed:19793753, PubMed:24089336). Main cells of the accessory glands of males (paragonial gland). No expression in females or embryos (PubMed:3135120, PubMed:20458515). Expression levels are highest in male adults with little to no expression until the late pupal stages (PubMed:3135120, PubMed:20458515). Sperm-bound protein is cleaved to release an active C-terminal peptide. Gradual release from stored sperm may function to prolong PMR and enhance male reproductive success. Viable and fertile (PubMed:19793753). Males are able to transfer sperm but can only induce weak PMR behaviors in females (PubMed:12897240, PubMed:19793753). Belongs to the Drosophila sex peptide family.