Sequence-specific RNA-binding protein that acts as a post-transcriptional repressor by binding the 3'-UTR of mRNA targets. Binds to an RNA consensus sequence, the Pumilio Response Element (PRE), 5'-UGUANAUA-3', that is related to the Nanos Response Element (NRE) (PubMed:1459455, PubMed:1576962, PubMed:9404893, PubMed:9660969, PubMed:22345517). Mediates post-transcriptional repression of transcripts via different mechanisms: acts via direct recruitment of deadenylase complexes leading to translational inhibition and mRNA degradation (By similarity). Also mediates deadenylation-independent repression by promoting accessibility of miRNAs (PubMed:22345517). Mediates post-transcriptional silencing of E2f mRNA by binding to its 3'-UTR and promoting miRNA regulation (PubMed:22345517). Required for abdominal development and to support proliferation and self-renewal of germ cells. Pum is the only gene required for nos activity that is not also required for posterior localization of germline determinants. Pum is required during embryogenesis when nos activity apparently moves anteriorly from the posterior pole (PubMed:1459455, PubMed:1576962, PubMed:9404893, PubMed:9660969). Interacts with nos and brat. Acts via the formation of a quaternary complex composed of pum, nos, brat and the 3'-UTR mRNA of hb. It is concentrated in the cortical region of the embryo beneath the nuclei. Expressed both maternally and zygotically in embryos. The pumilio repeats mediate the association with RNA by packing together to form a right-handed superhelix that approximates a half donut. RNA-binding occurs on the concave side of the surface. Pum is composed of 8 pumilio repeats of 36 residues; each repeat binds a single nucleotide in its RNA target. Residues at positions 12 and 16 of the pumilio repeat bind each RNA base via hydrogen bonding or van der Waals contacts with the Watson-Crick edge, while the amino acid at position 13 makes a stacking interaction. The recognition of RNA by pumilio repeats is base specific: cysteine and glutamine at position 12 and 16, respectively, bind adenine; asparagine and glutamine bind uracil; and serine and glutamate bind guanine. Flies display defective abdomen pattern formation and are embryonic lethal.