Differential promoter utilization by the bovine papillomavirus in transformed cells and productively infected wart...

Expression of the 'late' genes of bovine papillomavirus type 1 (BPV-1) occurs only in the differentiated keratinocytes of the productively infected fibropapilloma. A detailed analysis of viral transcription in the fibropapilloma was performed and compared to BPV-1 specific transcription in transformed C127 cells. A cDNA library was constructed from bovine fibropapilloma mRNA using the method of Okayama and Berg. Analysis of full length cDNAs showed that the majority of viral transcripts in the fibropapilloma have 5' termini near nt 7250 and utilize a common splice donor site at nt 7385. This mRNA start site was confirmed by the combination of primer extension and nuclease S1 analyses; it is not utilized in the BPV-1-transformed C127 cell, thus identifying it as a wart specific, 'late' promoter. Upstream of this mRNA start site is a tandemly repeated sequence element homologous to the SV40 late promoter sequence GGTACCTAACC, which has been shown to be important for the efficient utilization of the SV40 major late start site. Two additional mRNA start sites at nt 7185 and nt 7940 in the long control region (LCR) were identified and were found to be used in bovine warts as well as in BPV-1-transformed mouse cells. The promoter region upstream of the nt 7940 mRNA start site contains the E2 responsive enhancer mapping between nt 7611 and nt 7805 [Spalholz, B.A., Lambert, P.F., Yee, C. and Howley, P.M. (1987) J. Virol., in press].(ABSTRACT TRUNCATED AT 250 WORDS)