Puf repeats (aka PUM-HD, Pumilio homology domain) are necessary and sufficient for sequence specific RNA binding in fly Pumilio and worm FBF-1 and FBF-2. Both proteins function as translational repressors in early embryonic development by binding sequences in the 3' UTR of target mRNAs (e.g. the nanos response element (NRE) in fly Hunchback mRNA, or the point mutation element (PME) in worm fem-3 mRNA). Other proteins that contain Puf domains are also plausible RNA binding proteins. Swiss:P47135, for instance, appears to also contain a single RRM domain by HMM analysis. Puf domains usually occur as a tandem repeat of 8 domains. The Pfam model does not necessarily recognise all 8 repeats in all sequences; some sequences appear to have 5 or 6 repeats on initial analysis, but further analysis suggests the presence of additional divergent repeats. Structures of PUF repeat proteins show they consist of a two helix structure [3,4].

1: A conserved RNA-binding protein that regulates sexual fates in the C. elegans hermaphrodite germ line. Zhang B, Gallegos M, Puoti A, Durkin E, Fields S, Kimble J, Wickens MP. Nature 1997;390:477-484. PMID:9393998

2: The Pumilio protein binds RNA through a conserved domain that defines a new class of RNA-binding proteins. Zamore PD, Williamson JR, Lehmann R. RNA 1997;3:1421-1433. PMID:9404893

3: Structure of Pumilio reveals similarity between RNA and peptide binding motifs. Edwards TA, Pyle SE, Wharton RP, Aggarwal AK; Cell 2001;105:281-289. PMID:11336677

4: Crystal structure of a Pumilio homology domain. Wang X, Zamore PD, Hall TM; Mol Cell 2001;7:855-865. PMID:11336708

5: The PUF Protein Family: Overview on PUF RNA Targets, Biological Functions, and Post Transcriptional Regulation. Wang M, Oge L, Perez-Garcia MD, Hamama L, Sakr S; International Journal of Molecular Sciences 2018;19(2). PMID:29385744