Multiplecis-active elements in the long control region of bovine papillomavirus type 1 (BPV-1)

Abstract

A 1.0 kb region of the BPV-1 genome (the long control region, LCR), contains controls for transcription and the origin of replication. Transcription directed by the LCR is activated by the viral encoded E2 protein. To define the essential cis acting elements that are required to control transcription we have constructed a series of deletions throughout the LCR. We have identified three important domains in the LCR, two of which respond to E2. We have analysed the ability of small subcloned regions of the E2 responsive domains to act as enhancers in a heterologous assay system. This has led to the identification of five independent E2 responsive elements. We have shown that a fragment of only 38 base pairs is sufficient to respond to activation by E2. We also present evidence to suggest two types of E2 responsiveness that result in strong or weak activation. Strong response is correlated with the presence of the sequence 5'-ACCG/TNNNC/TCGGTGC-3' whereas weak response is correlated with the presence of a related sequence 5'-ACC(N)6GGT-3'. The contribution of these multiple elements to viral transcription is discussed.

The functional BPV-1 E2 trans-activating protein can act as a repressor by preventing formation of the initiation complex.

“…An interesting feature of trans-activation by E2 protein in vivo is that although E2 can bind strongly to a single palindromic site (Dostatni et al 1988;, this single site constitutes only a weak E2-dependent enhancer. A strong synergistic effect is observed between two sites either in m a m m a l i a n cells (Harrison et al 1987;Hawley-Nelson et al 1988;Spalholz et al 1988;Thierry et al 1990) or in yeast (Lambert et al 1989a;Morrissey et al 1989;Stanway et al 1989). To determine whether E2 transcriptional activation in vitro follows the same rules as in vivo, different test templates containing one, two, or six E2-binding sites were assayed for their in vitro E2-mediated stimulation.…”

Amino acids necessary for DNA contact and dimerization imply novel motifs in the papillomavirus E2 trans-activator.

“…This 410-amino-acid protein is responsible for the coordination of BPV transcription. E2 binds specifically and with high affinity to the palindrome ACCGN4CGGT (Androphy et al 1987;Moskaluk and Bastia 1988;Li et al 1989;Monini et al 1991) and activates transcription from promoters with these enhancer elements (Spalholz et al 1985;Harrison et al 1987;Haugen et al 1987;Hirochika et al 1987;Spalholz et al 1987;Gius et al 1988;HawleyNelson et al 1988;Moskaluk and Bastia 1988;Li et al 1989;Sousa et al 1990). Genetic studies predict that the ^These authors conttibuted equally to this work.…”

Kinetic and equilibrium binding studies of the human papillomavirus type-16 transcription regulatory protein E2 interacting with core enhancer elements

“…This motif has been found in the genomes of all papillomaviruses sequenced to date (14), and is repeated 17 times in the BPV-1 genome, 12 sites being clustered in the viral regulatory region or enhancer (URR), and at least one site being associated with each of the major viral promoters (15). In the bovine system, the E2 protein is a necessary activator of viral transcription capable of stimulating transcription from the BPV E2 conditional enhancer by 300-fold (16)(17)(18)(19)(20)(21). The protein is also required in association with the viral El protein for replication (22,23).…”