THE PAPILLOMAVIRUS MINOR CAPSID PROTEIN, L2, INDUCES LOCALIZATION OF THE MAJOR CAPSID PROTEIN, L1, AND THE VIRAL TRANSCRIPTION REPLICATION PROTEIN, E2, TO PML ONCOGENIC DOMAINS/

We have used immunofluorescent staining and confocal microscopy to exa mine the subcellular localization of structural and nonstructural bovi ne papillomavirus (BPV) proteins in cultured cells that produce infect ious virions. When expressed separately, L1, the major capsid protein, showed a diffuse nuclear distribution while L2, the minor capsid prot ein, was found to localize to punctate nuclear regions identified as p romonocytic leukemia protein (PML) oncogenic domains (PODs). Coexpress ion of L1 and L2 induced a relocation of L1 into the PODs, leading to the colocalization of L1 and L2. The effect of L2 expression on the di stribution of the nonstructural viral proteins E1 and E2, which are re quired for maintenance of the genome and viral DNA synthesis, was also examined. The localization of the E1 protein was unaffected by L2 exp ression. However, the pattern of anti-E2 staining was dramatically alt ered in L2-expressing cells. Similar to L1, E2 was shifted from a disp ersed nuclear locality into the PODs and colocalized with L2. The recr uitment of full-length E2 by L2 occurred in the absence of other viral components. L2 was shown previously to be essential for the generatio n of infectious BPV. Our present results provide evidence for a role f or L2 in the organization of virion components by recruiting them to a distinct nuclear domain. This L2-dependent colocalization probably se rves as a mechanism to promote the assembly of papillomaviruses either by increasing the local concentration of virion constituents or by pr oviding the physical architecture necessary for efficient packaging an d assembly. The data also suggest a role for a nonstructural viral pro tein, E2, in virion assembly, specifically the recruitment of the vira l genome to the sites of assembly, through its high-affinity interacti on with specific sequences in the viral DNA.