WT-501

A plaque morphology mutant (pm-522) of human papovavirus BK, which was rescued from a human papovavirus BK-induced hamster pineocytoma, was characterized and compared with a cloned wild-type virus (wt-501). Mutant pm-522 formed turbid plaques and grew more slowly than wt-501 in human embryonic kidney (HEK) cells. The immunofluorescence assay revealed that more HEK cells underwent abortive infection with pm-522 than with wt-501. Whereas wt-501 induced brain tumors and osteosarcomas, but no insulinomas, in hamsters, pm-522 induced brain tumors and insulinomas. The DNA of pm-522 was found by electrophoresis and electron microscopy to have a deletion (85 +/- 15 base pairs) and an insertion (40 +/- 10 base pairs) between map coordinates 0.708 and 0.725 from the endonuclease EcoRI cleavage site. These results demonstrate the presence of a viable deletion human papovarivus BK mutant capable of inducing insulinomas in hamsters.