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). Mediates post-transcriptional repression of transcripts via different mechanisms: acts via direct recruitment of the CCR4-POP2-NOT deadenylase leading to translational inhibition and mRNA degradation. Also mediates deadenylation-independent repression by promoting accessibility of miRNAs. Detected in embryonic male and female gonads, heart, liver and muscle. Detected in adult brain, testis, ovary, heart, lung, spleen, kidney and muscle. 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. PUM1 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.