TFIIH kinase places bivalent marks on the carboxy-terminal domain of RNA polymerase II.

Posttranslational modifications of the carboxy-terminal domain (CTD) of the largest subunit of RNA polymerase II (Pol II) specify a molecular recognition code that is deciphered by proteins involved in RNA biogenesis. The CTD is comprised of a repeating heptapeptide (Y(1)S(2)P(3)T(4)S(5)P(6)S(7)). Recently, phosphorylation of serine 7 was shown to be important for cotranscriptional processing of two snRNAs in mammalian cells. Here we report that Kin28/Cdk7, a subunit of the evolutionarily conserved TFIIH complex, is a Ser7 kinase. The ability of Kin28/Cdk7 to phosphorylate Ser7 is particularly surprising because this kinase functions at promoters of protein-coding genes, rather than being restricted to promoter-distal regions of snRNA genes. Kin28/Cdk7 is also known to phosphorylate Ser5 residues of the CTD at gene promoters. Taken together, our results implicate the TFIIH kinase in placing bivalent Ser5 and Ser7 marks early in gene transcription. These bivalent CTD marks, in concert with cues within nascent transcripts, specify the cotranscriptional engagement of the relevant RNA processing machinery.

Emerging Views on the CTD Code.

The C-terminal domain (CTD) of RNA polymerase II (Pol II) consists of conserved heptapeptide repeats that function as a binding platform for different protein complexes involved in transcription, RNA processing, export, and chromatin remodeling. The CTD repeats are subject to sequential waves of posttranslational modifications during specific stages of the transcription cycle. These patterned modifications have led to the postulation of the "CTD code" hypothesis, where stage-specific patterns define a spatiotemporal code that is recognized by the appropriate interacting partners. Here, we highlight the role of CTD modifications in directing transcription initiation, elongation, and termination. We examine the major readers, writers, and erasers of the CTD code and examine the relevance of describing patterns of posttranslational modifications as a "code." Finally, we discuss major questions regarding the function of the newly discovered CTD modifications and the fundamental insights into transcription regulation that will necessarily emerge upon addressing those challenges.

Sequence-specificity and energy landscapes of DNA-binding molecules.

A central goal of biology is to understand how transcription factors target and regulate specific genes and networks to control cell fate and function. An equally important goal of synthetic biology, chemical biology, and personalized medicine is to devise molecules that can regulate genes and networks in a programmable manner. To achieve these goals, it is necessary to chart the sequence specificity of natural and engineered DNA-binding molecules. Cognate site identification (CSI) is now achieved via unbiased, high-throughput platforms that interrogate an entire sequence space bound by typical DNA-binding molecules. Analysis of these comprehensive specificity profiles is facilitated through the use of sequence-specificity landscapes (SSLs). SSLs reveal new modes of sequence cognition and overcome the limitations of current approaches that yield amalgamated "consensus" motifs. The landscapes also reveal the impact of nonconserved flanking sequences on binding to cognate sites. SSLs also serve as comprehensive binding energy landscapes that provide insights into the energetic thresholds at which natural and engineered molecules function within cells. Furthermore, applying the CSI binding data to genomic sequence (genomescapes) provides a powerful tool for identification of potential in vivo binding sites of a given DNA ligand, and can provide insight into differential regulation of gene networks. These tools can be directly applied to the design and development of synthetic therapeutic molecules and to expand our knowledge of the basic principles of molecular recognition.

Chemical-genomic dissection of the CTD code.

Sequential modifications of the RNA polymerase II (Pol II) C-terminal domain (CTD) coordinate the stage-specific association and release of cellular machines during transcription. Here we examine the genome-wide distributions of the 'early' (phospho-Ser5 (Ser5-P)), 'mid' (Ser7-P) and 'late' (Ser2-P) CTD marks. We identify gene class-specific patterns and find widespread co-occurrence of the CTD marks. Contrary to its role in 3'-processing of noncoding RNA, the Ser7-P marks are placed early and retained until transcription termination at all Pol II-dependent genes. Chemical-genomic analysis reveals that the promoter-distal Ser7-P marks are not remnants of early phosphorylation but are placed anew by the CTD kinase Bur1. Consistent with the ability of Bur1 to facilitate transcription elongation and suppress cryptic transcription, high levels of Ser7-P are observed at highly transcribed genes. We propose that Ser7-P could facilitate elongation and suppress cryptic transcription.