A mutation in the DE loop of the VP1 protein that prevents polyomavirus transcription and replication

Natural mutants of the DE loop of the Polyomavirus (Py) major coat protein VP1 have been previously shown to display an altered host specificity (L. R icci, R. Maione, C. Passananti, A. Felsani, and P.Amati, 1992, J. Virol. 66 , 7153-7158). To better understand the role of this outfacing loop of the V P1 protein in Py infectivity, we constructed and characterized a Py mutant (Py M17) harboring a deletion of 7 AA within the tip of the DE loop. The mu tant virions obtained after DNA transfection were unable to replicate and i nitiate early transcription in fibroblast cells. Complementation experiment s performed to rescue the deficient M17 replication by means of wt function s revealed the cis-dominance of the mutation. In situ cell fractionation ex periments demonstrated that the Py mutant, like the Py wt, enters the cells , reaches the nucleus and that both the viral DNA and VP1 protein are found tightly bound to the nuclear matrix. These data suggest that the VP1 prote in, associated to the viral DNA, conditions early viral gene expression and that the DE loop of the protein must be involved in this process. (C) 2000 Academic Press.