The tissue specificity of both DNA replication and gene expression of Polyomavirus is to be studied in both in vitro and in vivo systems including infected mice. An emphasis will be to utilize homologous recombinant constructs so that cis interactions between the overlapping regulatory elements might be analyzed. The initial effort will be towards understanding the function of the Pvu II-4 region (N 5128 to 5262) in regulating tissue specificity. We have recently established that this element exerts both a negative (repressing) as well as positive (enhancing) regulatory effect in a tissue specific manner. The mechanism of this observation will be studied. The in vivo tissue specificity of these viable recombinants will then be compared to the specificity seen with trangenic mice to determine if the phenotype of the cis regulatory elements is independent of development and of chromosomal location. Finally, we will investigate the genetic determinants of papovirus species (as opposed to tissue) specific DNA replication. Using recombinants of SV40 and Polyoma virus, DNA regulation in both primate and murine cells will be studied.