Adapter protein that plays a central role in localization of transcripts in the oocyte and in young embryos (PubMed:9118812). Maintains RNA targets in a repressed state by promoting their deadenylation and protects deadenylated mRNAs from further degradation (PubMed:21937713). Binds to and recruits eIF-4E to the 3'-UTR of some mRNA targets which prevents interaction between eIF4E1 and eIF4G (PubMed:14685270, PubMed:15465908, PubMed:21081899). This may contribute to translational repression but does not appear to be necessary for it to occur (PubMed:21081899). Can promote translational repression independently of deadenylation and eIF4E1 binding (PubMed:21937713). Required for correct localization of eIF4E1 in the developing oocyte (PubMed:15465908). Required for translational repression of oskar (osk) mRNA (PubMed:14691132, PubMed:14723848). Also required for the translational repression of nanos (nos) mRNA (PubMed:21081899). Promotes the accumulation of the germ plasm components osk, vas and stau at the posterior pole of the oocyte and is required for germ cell development (PubMed:22454519, PubMed:17277377). Represses orb positive autoregulatory activity which prevents premature activation of orb and ensures its accumulation specifically in the developing oocyte (PubMed:22164257). In 0-1 hour embryos, forms a complex with me31B, cup, tral and pAbp which binds to various mRNAs including maternal mRNAs, and down-regulates their expression during the maternal-to-zygotic transition (PubMed:28875934). Component of the osk RNP complex, which is composed of at least exu, yps, aret/bruno, cup, and the mRNA of osk (PubMed:10662770). Interacts with the decapping activators me31B and tral (PubMed:21937713). Component of the nos RNP complex, which is composed of at least smg, cup, tral, me31B, the CCR4-NOT complex members Rga/NOT2 and Caf1, and the mRNA of nos (PubMed:21081899). Interacts with btz (PubMed:14691132, PubMed:14723848). Recruited to the 3'-UTR of nos and osk mRNAs by smg and btz, respectively (PubMed:14685270, PubMed:14691132). Forms a ribonucleoprotein complex (RNP) containing at least me31B, eIF4E1, cup, tral and pAbp; this interaction is required for the translational silencing of maternal mRNAs during the maternal-to-zygotic transition (PubMed:28875934). No interaction was detected with pAbp in 1-5 hour embryos (PubMed:28875934). Interacts with osk and vas (PubMed:22454519). Interacts with Pop2, twin/CCR4, Rga, Not3 and Not1 which are all core components of the CCR4-NOT deadenylase complex; interaction with the complex is required for cup deadenylation activity (PubMed:21937713). Interacts with nos (PubMed:11060247). Interacts with smg (PubMed:14685270). Interacts (via YXXXXLphi motifs) with eIF4E1; the interaction promotes retention of cup in the cytoplasm (PubMed:14723848, PubMed:14685270, PubMed:15465908, PubMed:21937713, PubMed:22832024). Interacts with orb; the interaction represses the orb positive autoregulatory loop (PubMed:22164257). Interacts with Nup154 (PubMed:17277377). Retained in the cytoplasm by interaction with eIF4E1. Located throughout the cytoplasm of all germline cells and is excluded from the nucleus of nurse cells, oocytes and follicular cells (PubMed:15465908). During oogenesis, accumulates in the cytoplasm at the posterior end of the forming oocyte (PubMed:15465908). Component of the germ plasm in developing oocytes (PubMed:22454519). Does not localizes in processing bodies (P-bodies) (PubMed:24335285). Predominantly expressed in ovaries and in 0-2 hours old embryos. Weakly expressed in testis. Expressed in young embryos through stage 9, then it decreases throughout the rest of embryogenesis. In ovaries, it is expressed in germ cells throughout pre-vitellogenic development, but is not expressed in the somatic follicle cells. In germarial cysts, the protein (and not the transcripts) is transported selectively into the oocyte. Expressed in the egg chamber and more specifically in nurse cells (at protein level) (PubMed:17277377). Expressed during the first 2 hours of embryogenesis but is absent in 2-5 hour embryos (at protein level) (PubMed:28875934). Expressed both maternally and zygotically (PubMed:9118812). Expressed throughout embryogenesis (PubMed:22454519). In stage 2, uniformly distributed throughout the whole embryo (PubMed:22454519). During blastoderm formation, concentrated at the posterior pole to become incorporated into newly formed germ cells (PubMed:22454519). Subsequently accumulates specifically in the pole cells at stage 10, when they migrate through the posterior midgut primordium, and during stage 14, when the germ cells reach their final destination (PubMed:22454519). The YXXXXLphi motifs mediate interaction with eIF4E1. Mislocalization and precocious expression of orb in the ovary, accumulation of high levels of orb in nurse cells, elongation of orb poly-A tails, hyperphosphorylation of orb and reduced osk mRNA levels (PubMed:22164257). Reduced number of germ cells (PubMed:22454519). Belongs to the 4E-T/EIF4E-T family. Extended N-terminus. Extended N-terminus.