Host range bias of the JC virus mutant enhancer with DNA rearrangement

JC-HEK, a JC virus (JCV) host range mutant adapted to growth in human embryonic kidney cells (HEK), has DNA rearrangement in the control region for early transcription. The 822-bp rearranged segment of JC-HEK (containing one authentic promoter-enhancer unit of 98 bp and truncated coding region of T-antigen and VP-1 genes) was inserted into pSV0cat vector and examined for expression of chloramphenicol acetyltransferase (CAT). The CAT activity induced by the mutant was comparable to that by the SV40 promoter-enhancer (pSV2cat) and four times as high as that by the prototype JCV (Mad-1) in HEK cells, whereas the two JCV promoter-enhancers were equally efficient in a permissive neuroblastoma cell line. On the other hand, both JC-HEK DNA with three DNA replication origins and Mad-1 DNAs replicated after transfection into HEK cells at a similar efficiency in the presence of JCV T-antigen. The elevated promotor-enhancer activity caused by the DNA rearrangement seems to play a major role in adaptation of JCV to growth in HEK cells.