During recent years, advances have been made in understanding the func
tions of the viral oncoproteins E6 and E7. E6 und E7 code for proteins
forming complexes with cellular proteins, which regulate the cell cyc
le. This leads to a disturbance of the physiological control mechanism
and to increased proliferation of the infected cells. Enhanced expres
sion of viral oncogenes in cells infected by genital ''high risk'' HPV
types results in chromosomal instability and in an accumulation of mu
tational events. Cutaneous HPV types apparently follow other strategie
s to transform their host cells.