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. 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].
Members of the Pumilio family of proteins (Puf) regulate translation and mRNA stability in a wide variety of eukaryotic organisms including mammals, flies, worms, slime mold, and yeast [PUBMED:10662662]. Pumilio family members are characterised by the presence of eight tandem copies of an imperfectly repeated 36 amino acids sequence motif, the Pumilio repeat, surrounded by a short N- and C-terminal conserved region. The eight repeats and the N- and C-terminal regions form the Pumilio homology domain (PUM-HD). The PUM-HD domain is a sequence-specific RNA binding domain. Several Puf members have been shown to bind specific RNA sequences mainly found in the 3' UTR of mRNA and repress their translation [PUBMED:14584586]. Frequently, Puf proteins function asymmetrically to create protein gradients, thus causing asymmetric cell division and regulating cell fate specification [PUBMED:1459455].
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Wang M, Oge L, Perez-Garcia MD, Hamama L, Sakr S;, International Journal of Molecular Sciences 2018;19(2).: The PUF Protein Family: Overview on PUF RNA Targets, Biological Functions, and Post Transcriptional Regulation. PUBMED:29385744 EPMC:29385744.