 Solution

About 80% of full-length-expressing biological cells have two conspicuous nuclear foci, whereas roughly 90% of biological cells expressing the deletion protein have none. Both proteins show nuclear fluorescence, so the result is not explained simply by complete exclusion of the deletion protein from the nucleus. The DNA-binding domain is needed for efficient focal accumulation at a small number of host sites. A plausible explanation is recognition of repeated host DNA sequences resembling the viral binding sites; clustered repeats and homotypic contacts would concentrate the protein enough to create visible foci.

Two spots are compatible with one locus on each homologous chromosome in a diploid biological cell. They do not prove diploidy, identify a chromosome, or exclude unresolved sister loci and cell-cycle effects. An alternative is DNA-dependent recruitment through a host complex. Matching protein abundance and confirming stability of the deletion construct would make the domain comparison stronger. Punctate fluorescence alone does not demonstrate a liquid condensate or show that a focus identifies an origin of replication.