Human U2 snRNA Genes Exhibit a Persistently Open Transcriptional State and Promoter Disassembly at Metaphase

Abstract

In mammals, small multigene families generate spliceosomal U snRNAs that are nearly as abundant as rRNA. Using the tandemly repeated human U2 genes as a model, we show by footprinting with DNase I and permanganate that nearly all sequences between the enhancer-like distal sequence element and the initiation site are protected during interphase whereas the upstream half of the U2 snRNA coding region is exposed. We also show by chromatin immunoprecipitation that the SNAPc complex, which binds the TATA-like proximal sequence element, is removed at metaphase but remains bound under conditions that induce locus-specific metaphase fragility of the U2 genes, such as loss of CSB, BRCA1, or BRCA2 function, treatment with actinomycin D, or overexpression of the tetrameric p53 C terminus. We propose that the U2 snRNA promoter establishes a persistently open state to facilitate rapid reinitiation and perhaps also to bypass TFIIH-dependent promoter melting; this open state would then be disassembled to allow metaphase chromatin condensation.

ACKNOWLEDGMENTS

We thank Michelle Baranski and Steve Hauschka for help with quantitative PCR; Denise Galloway for the PG-13/htert retrovirus; Brian Kennedy for WI38 cells; Piri Welcsh and Mary-Claire King for BRCA1- and BRCA2-deficient cell lines; and Nouria Hernandez for SNAPc 43 and 190 antibodies.

This work was supported by Public Health Service award GM-41624 from the National Institutes of Health.