The Protein Kinase CK2 Phosphorylates SNAP190 to Negatively Regulate SNAPC DNA Binding and Human U6 Transcription by RNA Polymerase III

Abstract

In humans, polymerase specificity for snRNA 2 gene transcription depends upon the architecture of the core promoter region. snRNA genes containing solely a proximal sequence element (PSE) are transcribed by RNA polymerase II, whereas those containing juxtaposed PSE and TATA box elements are transcribed by RNA polymerase III (1). The human small nuclear RNA-activating protein complex (SNAP C ) is a general transcription factor that coordinates human snRNA gene transcription for both polymerases (2) through its ability to bind to the PSE (3), while serving as a target for numerous regulatory factors that influence snRNA gene transcription. SNAP C , also known as PTF (4), consists of five subunits called SNAP190 (PTF␣), SNAP50 (PTF␤), SNAP45 (PTF␦), SNAP43 (PTF␥), and SNAP19 (2, 5-10). Within this complex, PSE-specific binding is mediated by two of these factors SNAP190, which contains a Myb DNA binding domain (5), and SNAP50, which contains an unorthodox, but evolutionarily conserved zinc finger DNA binding domain (11). Neither SNAP190 nor SNAP50 can bind DNA alone, but instead are coordinated by SNAP43, which interacts with both factors to facilitate formation of a complex that is capable of DNA binding (12,13).In addition to its role in PSE recognition, SNAP190 plays a pivotal role in snRNA gene transcription by interacting with the TATA-box-binding protein (TBP), stimulating TBP promoter recruitment to TATA-box containing snRNA genes (14). Two regions within SNAP190 have been defined as playing a role in TBP recruitment. One TBP recruitment region (TRR1) is located toward the N terminus (15) and is adjacent to the region involved in SNAP C assembly with SNAP19 and SNAP43 (16). A second TBP recruitment region (TRR2) is located within the Myb DNA binding domain and was proposed to interact with the TBP DNA binding domain (13); these interactions are likely stabilized by adjacent binding of both factors at the PSE and TATA box, respectively. SNAP190 is also a direct target of the transcriptional activator protein Oct-1 (17, 18), which binds to an octamer sequence in the distal sequence element of human snRNA genes.As a central player in snRNA gene transcription, SNAP190 is also targeted for regulation through post-translational modification. For example, SNAP190 is phosphorylated both in vivo and in vitro, and in part, phosphorylation is mediated by the protein kinase CK2 that associates with and phosphorylates the N-terminal half of SNAP190 predominately at serine residues (19). CK2 associates with other components of the RNA polymerase III transcriptional machinery, including the Brf1-TFIIIB complex (20), as well as with RNA polymerase III itself (21). The functional consequences of CK2 association with these components of the RNA polymerase III transcriptional machinery are complex. CK2 phosphorylation of RNA polymerase III stimulates U6 snRNA gene transcription (21); however, during mitosis CK2 can instead down-regulate U6 transcription by phosphorylating Bdp1 (22), a component shared by both Brf1-TFIIIB and B...

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Towards an understanding of regulating Cajal body activity by protein modification

“…For example, it has been shown that CK2 phosphorylates SNAP190, which in turn regulates SNAPc complex binding and transcription of the U6 snRNA gene by RNA polymerase III. 169 Clearly, therefore, the post-translational regulation of these 3 transcription complexes is largely unchartered territory and fertile ground for investigation.…”

Transcriptional regulation of human small nuclear RNA genes

“…The loss of promoter association by Bdp1 is sufficient to explain M-phase repression of snRNA expression. Although less pronounced, SNAP C promoter association is also diminished during M-phase [87], and may be attributable to CK2 phosphorylation of SNAP190 at a serine-rich region located adjacently to its Myb-DNA binding domain, which inhibits SNAP C recognition of the PSE [100].…”