THE T T COMMON EXON OF SIMIAN-VIRUS-40, JC, AND BK POLYOMAVIRUS-T ANTIGENS CAN FUNCTIONALLY REPLACE THE J-DOMAIN OF THE ESCHERICHIA-COLI DNAJ MOLECULAR CHAPERONE/

The N-terminal 70 residue ''J-domain'' of the Escherichia coil DnaJ mo lecular chaperone is the defining and highly conserved feature of a la rge protein family. Based upon limited, yet significant, amino acid se quence homology to the J-domain, the DNA encoding the T/t common exon of the simian virus 40 (SV40), JC, or BK polyoma virus T antigen oncop roteins was used to construct J-domain replacement chimeras of the E. coil DnaJ chaperone. The virally encoded J-domains successfully substi tuted for the bacterial counterpart in vivo as shown by (i) complement ation for viability at low and high temperature of a hypersensitive ba cterial reporter strain, and (ii) the restoration of bacteriophage lam bda plaque forming ability in the same strain. The amino acid change, H42Q, in the SV40 T/t and the JC virus T/t exon, which is positionally equivalent to the canonical dnaJ259 H33Q mutation within the E. coil J-domain, entirely abolished complementing activity. These results str ongly suggest that the heretofore functionally undefined viral T/t com mon exon represents a bona fide J-domain that preserves critical featu res of the characteristic domain fold essential for J-domain interacti on with the ATPase domain of the Hsp70 family. This finding has implic ations for the regulation of DNA tumor virus T antigens by molecular c haperones.