Mouse anti-Human BRF1 monoclonal antibody, clone 3F0

Adenylate-uridylate (AU)-rich elements (AREs) are sequence instability elements that are known to be located in the 3' untranslated regions (UTR) in thousands of human transcripts. AREs regulate the expression of many genes at the post-transcriptional level, and they are essential for many normal cellular functions. We conducted a transcriptome-wide screen for AREs and found that they are most abundant in introns, with up to 25% of introns containing AREs corresponding to 58% of human genes. Clustering studies of ARE size, complexity, and distribution revealed that, in introns, longer AREs with two or more overlapping repeats are more abundant than in the 3'UTR, and only introns can contain very long AREs with 6-14 overlapping AUUUA pentamers. We found that intronic sites of the ARE binding proteins HuR/ELAVL1, ZFP36/TTP, AUF1, and BRF1/ZFP36L1 overlap with the intronic AREs with HuR being most abundant. Accordingly, RNA-IP experiments demonstrated a specific association of HuR with reporter and endogenous pre-mRNAs that contain intronic AREs. Moreover, HuR knockdown led to a significant general reduction in the mRNA levels of genes that contain intronic AREs and to a specific reduction in the expression of ARE-intronic reporters. The data represent bioinformatics analysis for key RNA-binding proteins interactions with intronic AREs and provide experimental evidence for HuR binding to AREs. The widespread distribution of intronic AREs and their particular association with HuR and HuR binding sites indicates that more than half of human genes can be regulated post-transcriptionally by AREs.

The Brf1 subunit of TFIIIB plays an important role in recruiting the TATA-binding protein (TBP) to the upstream region of genes transcribed by RNA polymerase III. When TBP is not bound to promoters, it sequesters its DNA binding domain through dimerization. Promoter assembly factors therefore might be required to dissociate TBP into productively binding monomers. Here we show that Saccharomyces cerevisiae Brf1 induces TBP dimers to dissociate. The high affinity TBP binding domain of Brf1 is not sufficient to promote TBP dimer dissociation but in addition requires the TFIIB homology domain of Brf1. A model is proposed to explain how two distinct functional domains of Brf1 work in concert to dissociate TBP into monomers.