TFS and Spt4/5 accelerate transcription through archaeal histone-based chromatin.

Abstract

RNA polymerase must surmount translocation barriers for continued transcription. In Eukarya and most Archaea, DNA-bound histone proteins represent the most common and troublesome barrier to transcription elongation. Eukaryotes encode a plethora of chromatin-remodeling complexes, histone-modification enzymes and transcription elongation factors to aid transcription through nucleosomes, while archaea seemingly lack machinery to remodel/modify histone-based chromatin and thus must rely on elongation factors to accelerate transcription through chromatin-barriers. TFS (TFIIS in Eukarya) and the Spt4-Spt5 complex are universally encoded in archaeal genomes, and here we demonstrate that both elongation factors, via different mechanisms, can accelerate transcription through archaeal histone-based chromatin. Histone proteins in Thermococcus kodakarensis are sufficiently abundant to completely wrap all genomic DNA, resulting in a consistent protein barrier to transcription elongation. TFS-enhanced cleavage of RNAs in backtracked transcription complexes reactivates stalled RNAPs and dramatically accelerates transcription through histone-barriers, while Spt4-Spt5 changes to clamp-domain dynamics play a lesser-role in stabilizing transcription. Repeated attempts to delete TFS, Spt4 and Spt5 from the T. kodakarensis genome were not successful, and the essentiality of both conserved transcription elongation factors suggests that both conserved elongation factors play important roles in transcription regulation in vivo, including mechanisms to accelerate transcription through downstream protein barriers.