The Werner syndrome protein is involved in RNA polymerase II transcription

Werner syndrome (WS) is a human progeroid syndrome characterized by the ear ly onset of a large number of clinical features associated with the normal aging process. The complex molecular and cellular phenotypes of WS involve characteristic features of genomic instability and accelerated replicative senescence. The gene involved (WRN) was recently cloned, and its gene produ ct (WRNp) was biochemically characterized as a helicase. Helicases play imp ortant roles in a variety of DNA transactions, including DNA replication, t ranscription, repair, and recombination. We have assessed the role of the W RN gene in transcription by analyzing the efficiency of basal transcription in WS lymphoblastoid cell lines that carry homozygous WRN mutations. Trans cription was measured in permeabilized cells by [H-3]UTP incorporation and in vitro by using a plasmid template containing the RNA polymerase II (RNA pol II)-dependent adenovirus major late promoter. With both of these approa ches, we find that the transcription efficiency in different WS cell lines is reduced to 40-60% of the transcription in cells from normal individuals. This defect can be complemented by the addition of normal cell extracts to the chromatin of WS cells. Addition of purified wild-type WRNp but not mut ated WRNp to the in vitro transcription assay markedly stimulates RNA pol I I-dependent transcription carried out by nuclear extracts. A nonhelicase do main (a direct repeat of 27 amino acids) also appears to have a role in tra nscription enhancement, as revealed by a yeast hybrid-protein reporter assa y. This is further supported by the lack of stimulation of transcription wh en mutant WRNp lacking this domain was added to the in vitro assay. We have thus used several approaches to show a role for WRNp in RNA pol II transcr iption, possibly as a transcriptional activator. A deficit in either global or regional transcription in WS cells may be a primary molecular defect re sponsible for the WS clinical phenotype.