COMPETENT TRANSCRIPTION INITIATION BY RNA-POLYMERASE-II IN CELL-FREE-EXTRACTS FROM XERODERMA-PIGMENTOSUM GROUP-B AND GROUP-D IN AN OPTIMIZED RNA-TRANSCRIPTION ASSAY

The human autosomal recessive disease, xeroderma pigmentosum (XP), can result from mutations in any one of seven genes, designated XPA throu gh XPG. Of these, the XPB and XPD genes encode proteins that are subun its of a general transcription factor, TFIIH, involved in both nucleot ide excision repair (NER) and initiation of mRNA transcription by RNA polymerase II. In humans, mutation of the XPB or XPD gene impairs NER, resulting in hyper-sensitivity to sunlight and greatly increased skin tumor formation. However, no transcription deficiency has been demons trated in either XP-B or XP-D. We have employed an optimized cell-free RNA transcription assay to analyze transcription activity of XP-B and XP-D. Although the growth rate was normal, the XP-B and XP-D cells co ntained reduced amounts of TFIIH. Extracts prepared from XP-B and XP-D lymphoblastoid cells exhibited similar transcription activity from th e adenovirus major late promoter when compared to that in extracts fro m normal cells. Thus, we conclude that the XP-B and XP-D lymphoblastoi d cells do not have impaired RNA transcription activity. We consider t he possible consequences of the reduced cellular content of TFIIH for the clinical symptoms in XP-B or XP-D patients, and discuss a 'conditi onal phenotype' that may involve an impairment of cellular function on ly under certain growth conditions. (C) 1997 Elsevier Science B.V.