AN ANTISENSE PROMOTER WITHIN THE HEPATITIS-B VIRUS-X GENE

Sequences of the Hepatitis B virus X (HBx) gene are preferentially ret ained on chromosomally integrated viral DNA and thereby the precore/co re promoter as a part of its reading frame, The existence of a second promoter mapping to the same DNA region is suggested by an antisense ( AS) RNA which has been described earlier by Standring's group, Here, t he capacity of sequences upstream to this AS RNA to function as a bidi rectional promoter was analyzed. On a cloned monomer of viral DNA a se gment spanning the start codon of the HBx gene and a site within the H Bx frame was replaced by a luciferase reporter gene (Photinus pyralis) plus a downstream polyadenylation signal of SV40 origin. Insertion in HBx and AS orientation allowed to compare the apparent strengths of t he respective promoter activities. Both DNA constructs expressed lucif erase to levels above the one induced by a reference plasmid expressin g the gene under control of the SV40 promoter. In the context of a rep orter plasmid a 241-bp subregion of the HBx gene with enhancer II in i ts center part functioned bidirectionally as AS and as core promoter. For the expression of a putative AS factor two effector plasmids drive n by the autologous and a heterologous promoter, respectively, were es tablished which stimulated in co-transfection experiments a c-myc targ et gene to a higher degree than a corresponding HBx effector construct .