Chromatin-based transcriptional punctuation

Abstract

The long polycistronic transcription units of trypano- somes do not appear to be demarcated by the usual DNA motifs that punctuate transcription in familiar eukar- yotes. In this issue of Genes & Development, Siegel and colleagues (pp. 1063-1076) describe a system for the demarcation of trypanosome transcription units based on the deposition and turnover of histone variants rather than on the binding of transcription factors. Replication- independent incorporation of histone variants and de- stabilization of nucleosomes is an emerging theme at promoters of more familiar eukaryotes, and it now appears that this system is an evolutionarily conserved mode of transcriptional punctuation. © 2009 by Cold Spring Harbor Laboratory Press ISSN. .