Mapping of monoclonal antibody epitopes in the nucleolar protein fibrillarin (B-36) of Physarum polycephalum.

We have mapped the epitopes for nine monoclonal antibodies raised against the nucleolar protein fibrillarin of the slime mold Physarum polycephalum. This has been done using a combination of specific chemical and enzymatic cleavage, Western blotting and partial sequencing of fragments. Cleavage with cyanogen bromide reveals four prominent methionine cleavage sites within the protein. Western blotting shows that none of the monoclonal antibody epitopes are dependent on long range interactions. Eight highly-conserved epitopes are clustered in the carboxy terminal half of the protein, while a single less-conserved epitope (for monoclonal antibody P1G12) is located at the amino terminus and appears to lie within the Gly/DMA/Phe domain.