CHARACTERIZATION OF THE DNA-BINDING PROPERTIES OF POLYOMAVIRUS CAPSIDPROTEINS

The DNA binding properties of the polyomavirus structural proteins VPI , VP2, and VP3 were studied by Southwestern analysis. The major viral structural protein VP1 and host-contributed histone proteins of polyom avirus virions were shown to exhibit DNA binding activity, but the min or capsid proteins VP2 and VP3 failed to bind DNA. The N-terminal firs t five amino acids (Ala-1 to Lys-5) were identified as the VP1 DNA bin ding domain by genetic and biochemical approaches. Wild-type VP1 expre ssed in Escherichia coli (RK1448) exhibited DNA binding activity, but the N-terminal truncated VP1 mutants (lacking Ala-1 to Lys-5 and Ala-1 to Cys-11) failed to bind DNA. The synthetic peptide (Ala-1 to Cys-11 ) was also shown to have an affinity for DNA binding. Site-directed mu tagenesis of the VP1 gene showed that the point mutations at Pro-2, Ly s-3, and Arg-4 on the VP1 molecule did not affect DNA binding properti es but that the point mutation at Lys-5 drastically reduced DNA bindin g affinity. The N-terminal (Ala-1 to Lys-5) region of VP1 was found to be essential and specific for DNA binding, while the DNA appears to b e non-sequence specific. The DNA binding domain and the nuclear locali zation signal are located in the same N-terminal region.