Functional organization of the HPyV genome. The viral genome consists of a circular dsDNA of ~5,000 base pairs. It can be divided into the noncoding control region (NCCR) flanked by the early and late regions. The NCCR encompasses the origin of replication and the early and late promoter elements. The early region, predominantly expressed before viral DNA replication, encodes the large T-antigen (LT-ag) and small t-antigen (st-ag). The late region is expressed late in the viral life cycle and codes for the capsid proteins VP1, VP2, and VP3. Some HPyV encode additional early proteins and the late protein, agnoprotein. The early and late genes are transcribed in opposite direction and from complementary DNA strands.
