Sequence reiteration required for the efficient growth of BK virus

Compared with wild-type BK virus DNA having tandem triplication of a 68 base pair (bp) element in its transcriptional control region, a mutant viral DNA with a single copy of the 68 bp element induced remarkably delayed virus production in human embryonic kidney (HEK) cells. We molecularly cloned the DNA of progeny viruses using plasmid vector pAT153. Nucleotide sequence analysis of representative clones revealed that all of the altered viral DNAs examined duplicated various segments extending over origin-distal portions of the 68 bp element and their flanking regions. After transfection of HEK cells, most of these rearranged viral DNAs induced viral growth slightly slower than, or at the same rate as, the wild-type viral DNA. Comparison of the structures of these rearranged viral DNAs suggests that reiteration of a 13 bp sequence, which is located in an origin-distal portion of the 68 bp element, is required for the efficient replication of BK virus.