Structure of yeast poly(A) polymerase alone and in complex with 3'-dATP.

Polyadenylate [poly(A)] polymerase (PAP) catalyzes the addition of a polyadenosine tail to almost all eukaryotic messenger RNAs (mRNAs). The crystal structure of the PAP from Saccharomyces cerevisiae (Pap1) has been solved to 2.6 angstroms, both alone and in complex with 3'-deoxyadenosine triphosphate (3'-dATP). Like other nucleic acid polymerases, Pap1 is composed of three domains that encircle the active site. The arrangement of these domains, however, is quite different from that seen in polymerases that use a template to select and position their incoming nucleotides. The first two domains are functionally analogous to polymerase palm and fingers domains. The third domain is attached to the fingers domain and is known to interact with the single-stranded RNA primer. In the nucleotide complex, two molecules of 3'-dATP are bound to Pap1. One occupies the position of the incoming base, prior to its addition to the mRNA chain. The other is believed to occupy the position of the 3' end of the mRNA primer.

Fip1 regulates the activity of Poly(A) polymerase through multiple interactions.

Fip1 is an essential component of the Saccharomyces cerevisiae polyadenylation machinery and the only protein known to interact directly with poly(A) polymerase (Pap1). Its association with Pap1 inhibits the extension of an oligo(A) primer by limiting access of the RNA substrate to the C-terminal RNA binding domain (C-RBD) of Pap1. We present here the identification of separate functional domains of Fip1. Amino acids 80 to 105 are required for binding to Pap1 and for the inhibition of Pap1 activity. This region is also essential for viability, suggesting that Fip1-mediated repression of Pap1 has a crucial physiological function. Amino acids 206 to 220 of Fip1 are needed for the interaction with the Yth1 subunit of the complex and for specific polyadenylation of the cleaved mRNA precursor. A third domain within amino acids 105 to 206 helps to limit RNA binding at the C-RBD of Pap1. Our data demonstrate that the C terminus of Fip1 is required to relieve the Fip1-mediated repression of Pap1 in specific polyadenylation. In the absence of this domain, Pap1 remains in an inhibited state. These findings show that Fip1 has a crucial regulatory function in the polyadenylation reaction by controlling the activity of poly(A) tail synthesis through multiple interactions within the polyadenylation complex.

Processivity of the Saccharomyces cerevisiae poly(A) polymerase requires interactions at the carboxyl-terminal RNA binding domain.

The interaction of the Fip1 subunit of polyadenylation factor I with the Saccharomyces cerevisiae poly(A) polymerase (PAP) was assayed in vivo by two-hybrid analysis and was found to involve two separate regions on PAP, located at opposite ends of the protein sequence. In vitro, Fip1 blocks access of the RNA primer to an RNA binding site (RBS) that overlaps the Fip1 carboxy-terminal interaction region and, in doing so, shifts PAP to a distributive mode of action. Partial truncation of this RBS has the same effect, indicating that this site is required for processivity. A comparison of the utilization of ribo- and deoxyribonucleotides as substrates indicates the existence on PAP of a second RBS which recognizes the last three nucleotides at the 3' end of the primer. This site discriminates against deoxyribonucleotides at the 3' end, and interactions at this site are not affected by Fip1. Further analysis revealed that the specificity of PAP for adenosine is not simply a function of the ATP binding site but also reflects interactions with bases at the 3' end of the primer and at another contact site 14 nucleotides upstream of the 3' end. These results suggest that the unique specificity of PAP for ribose and base, and thus the extent and type of activity with different substrates, depends on interactions at multiple nucleotide binding sites.

Pta1, a component of yeast CF II, is required for both cleavage and poly(A) addition of mRNA precursor.

CF II, a factor required for cleavage of the 3' ends of mRNA precursor in Saccharomyces cerevisiae, has been shown to contain four polypeptides. The three largest subunits, Cft1/Yhh1, Cft2/Ydh1, and Brr5/Ysh1, are homologs of the three largest subunits of mammalian cleavage-polyadenylation specificity factor (CPSF), an activity needed for both cleavage and poly(A) addition. In this report, we show by protein sequencing and immunoreactivity that the fourth subunit of CF II is Pta1, an essential 90-kDa protein originally implicated in tRNA splicing. Yth1, the yeast homolog of the CPSF 30-kDa subunit, is not detected in this complex. Extracts prepared from pta1 mutant strains are impaired in the cleavage and the poly(A) addition of both GAL7 and CYC1 substrates and exhibit little processing activity even after prolonged incubation. However, activity is efficiently rescued by the addition of purified CF II to the defective extracts. Extract from a strain with a mutation in the CF IA subunit Rna14 also restored processing, but extract from a brr5-1 strain did not. The amounts of Pta1 and other CF II subunits are reduced in pta1 strains, suggesting that levels of the subunits may be coordinately regulated. Coimmunoprecipitation experiments indicate that the CF II in extract can be found in a stable complex containing Pap1, CF II, and the Fip1 and Yth1 subunits of polyadenylation factor I. While purified CF II does not appear to retain the association with these other factors, this larger complex may be the form recruited onto pre-mRNA in vivo. The involvement of Pta1 in both steps of mRNA 3'-end formation supports the conclusion that CF II is the functional homolog of CPSF.

A new class of Spiegelmers containing 2'-fluoro-nucleotides.

Synthesis of 2'-fluoro-nucleosides from L-arabinose in order to perform the synthesis of 2'-fluoro-Spiegelmers binding to a neuropeptide.

Anti-ghrelin Spiegelmer NOX-B11 inhibits neurostimulatory and orexigenic effects of peripheral ghrelin in rats.

BACKGROUND AND AIMS: Ghrelin, the natural ligand of the growth hormone secretagogue receptor 1a, is the most powerful peripherally active orexigenic agent known. In rodents, ghrelin administration stimulates growth hormone release, food intake, and adiposity. Because of these effects, blocking of ghrelin has been widely discussed as a potential treatment for obesity. Spiegelmer NOX-B11 is a synthetic l-oligonucleotide, which was previously shown to bind ghrelin. We examined the effects of NOX-B11 on ghrelin induced neuronal activation and food intake in non-fasted rats. METHODS: Animals received various doses of NOX-B11, inactive control Spiegelmer, or vehicle intravenously. Ghrelin or vehicle was administered intraperitoneally 12 hours later and food intake was measured over four hours. Neuronal activation was assessed as c-Fos-like immunoreactivity in the arcuate nucleus. RESULTS: Treatment with NOX-B11 30 nmol suppressed ghrelin induced c-Fos-like immunoreactivity in the arcuate nucleus and blocked the ghrelin induced increase in food intake within the first half hour after ghrelin injection (mean 1.13 (SEM 0.59) g/kg body weight; 4.94 (0.63) g/kg body weight versus 0.58 (0.58) g/kg body weight; p<0.0001). Treatment with NOX-B11 1 nmol or control Spiegelmer had no effect whereas treatment with NOX-B11 10 nmol showed an intermediate effect on ghrelin induced food intake. CONCLUSIONS: Spiegelmer NOX-B11 suppresses ghrelin induced food intake and c-Fos induction in the arcuate nucleus in rats. The use of an anti-ghrelin Spiegelmer could be an innovative new approach to inhibit the biological action of circulating ghrelin. This may be of particular relevance to conditions associated with elevated plasma ghrelin, such as the Prader-Willi syndrome.