The X gene of hepatitis B virus shows a high level stimulation of the Roussarcoma virus long terminal repeat in the methylotropic yeast, Pichia pastoris

In order to studs the transactivational property of the X gene in the methy lotropic yeast Pichia pastor is, a Rous sarcoma virus-chloramphenicol acety ltransferase (RSV-CAT) cassette was co-transformed and integrated into the host yeast strain as a reporter which showed an overwhelming CAT activity. Immunoprecipitation of the yeast cell extracts with an X-specific monoclona l antibody, however, showed a low level expression of the X gene. Therefore besides a trans-effect of the X protein, the enhanced reporter activity co uld be a manifestation of a cis-effect of the X gene sequences also, Theref ore, unlike the transactivation studies with X gene in animal cells where l imited functional activity is observed, P. pastoris appears to be an excell ent system to study cis- and trans-aspects of gene regulation by the X gene . (C) 1999 Federation of European Biochemical Societies.