In higher eukaryotes, RNA Polymerase II (Pol II) pausing is a critical regulation mechanism controlling development, differentiation, proliferation, immune response, and all variety of cell function. Dysfunction of the regulation will lead to developmental defects, irregular immune responses, cancers, accelerating aging, and different diseases. A major portion (over ~30%) of genes in higher eukaryotes (in human and mice, not in yeast) are regulated by Pol II pausing. The release of paused Pol II at the +1 nucleosome is thought to require phosphorylation of C-terminal domain (CTD) of Pol II, NELF, and DSIF by CDK9. However, the precise role of phosphorylation of CTD of Pol II by CDK9 in Pol II pausing regulation is not well understood, nor if other mechanisms for pause release also contribute. In this proposal, we are proposing an innovative new idea that, if correct, will be paradigm changing. That is that in addition to the known mechanisms for pause release, JMJD5 is recruited by Pol II with Ser2 phosphorylation of CTD generated by CDK9 to carry out its proteolytic function on arginine methylated histone tails to generate “Tailless Nucleosomes” at +1 from TSS for paused Pol II to overcome. The phenomenon of clipping of histone tails and high turnover rate of histone was reported more than three decades ago; however, this process is still poorly understood in part due to the lack of identified enzymes responsible for the clipping process. Despite the confirmed importance of methylation of histone arginines in transcriptional regulation, the exact function of this modification is not very well understood. At the same time, the identities of histone arginine demethylases have remained elusive, though some candidates have been assigned. We propose that arginine methylation on nucleosomes at +1 from TSS represent a marker for genes regulated by paused Pol II. Furthermore, a group of Jumonji C (JmjC) domain containing protein family could specifically clip histone tails with methylated arginines on these nucleosomes. In the past two decades, we and other researchers have revealed that the JmjC domain family members have diverse enzymatic activities. Overall, these functions are related to the JmjC/cupin-like dioxygenase domains that are the hallmark of this protein family. We now have growing evidence that a subgroup of JmjC domain family, including JMJD5, JMJD7, and possibly others, may remove histone tails with methylated arginines through novel endopeptidase and aminopeptidase activities. We claimed that there exists a third protease family in life science with both endopeptidase and exopeptidase activities. Our preliminary functional data strongly suggests that JMJD5 and JMJD7 specifically recognize methylated arginines and make cleavages in the context of histone tails. Our structural analysis of JMJD5 and JMJD7 with and without substrates revealed unique features and surface charge distribution properties of these proteins that may account f...