Rtf1 is a conserved RNA polymerase II (RNAPII) elongation factor that promotes cotranscriptional histone modification, RNAPII transcript elongation, and mRNA processing. Rtf1 function requires the phosphorylation of Spt5, an essential RNAPII processivity factor. Spt5 is phosphorylated within its C-terminal domain (CTD) by cyclin-dependent kinase 9 (Cdk9), the catalytic component of positive transcription elongation factor b (P-TEFb). Rtf1 recognizes phosphorylated Spt5 (pSpt5) through its Plus3 domain. Since Spt5 is a unique target of Cdk9 and Rtf1 is the only known pSpt5-binding factor, the Plus3/pSpt5 interaction is thought to be a key Cdk9-dependent event regulating RNAPII elongation. Here, we dissect Rtf1 regulation by pSpt5 in the fission yeast Schizosaccharomyces pombe. We demonstrate that the Plus3 domain of Rtf1 (Prf1 in S. pombe) and pSpt5 are functionally distinct and that they act in parallel to promote Prf1 function. This alternate Plus3 domain function involves an interface that overlaps the pSpt5-binding site and that can interact with single-stranded nucleic acid or with the polymerase-associated factor (PAF) complex in vitro. We further show that the C-terminal region of Prf1, which also interacts with PAF, has a similar parallel function with pSpt5. Our results elucidate unexpected complexity underlying Cdk9-dependent pathways that regulate transcription elongation.

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Targeting allosteric sites at M muscarinic acetylcholine receptors is a promising strategy for the treatment of Alzheimer's disease. Positive allosteric modulators not only may potentiate binding and/or signaling of the endogenous agonist acetylcholine (ACh) but also may possess direct agonist activity (thus referred to as PAM-agonists). Recent studies suggest that PAM-agonists with robust intrinsic efficacy are more likely to produce adverse effects in vivo. Herein we present the synthesis and pharmacological evaluation of a series of pyrrole-3-carboxamides with a diverse range of allosteric profiles. We proposed structural modifications at top, core, or pendant moieties of a prototypical molecule. Although generally there was a correlation between the degree of agonist activity and the modulatory potency of the PAMs, some derivatives displayed weak intrinsic efficacy yet maintained strong allosteric modulation. We also identified molecules with the ability to potentiate mainly the affinity or both affinity and efficacy of ACh.