TFIIS Background Information
RNA polymerase II (RNAP II) comprises a 12 subunit protein complex that mediates transcription (1). RNAP II contains a unique carboxy terminal domain (CTD), which consists of 52 repeats of the consensus heptapeptide Tyr-Ser-Pro-Thr-Ser-Pro-Ser (1). The RNAP II isoform with an unphosphorylated CTD associates with transcription initiation complexes, whereas the isoform with a phosphorylated CTD is involved in transcription elongation (1-3). Transcription elongation by RNAP II can be interrupted by various obstacles, including certain DNA sequences, DNA binding proteins, chromatin, and DNA lesions (4). Bypass of many of these impediments depends upon the transcription elongation factor SII (TFIIS), which cleaves the nascent transcript and promotes read-through past the block (4,5). In Saccharomyces cerevisiae, the PPR2 genes encodes the TFIIS protein, which consists of three domains (5,6). Characterization of Domains II and III, which represent the portion of the TFIIS protein necessary for elongation, show that they comprise a three-helix bundle and a zinc ribbon motif, respectively, joined by a linker region (6,7). Yeast cells lacking TFIIS grow slowly and display defects in mRNA metabolism (8).
