N promotes transcription repression, probably by binding to the chromatin. A) The BSA standard marker quantified the concentration of purified N protein in SDS-PAGE. B) SDS-PAGE shows the expression of the purified histone protein from BL21 (DE3) pLysS cells, staining by Coomassie brilliant blue (CBB). C) The corresponding octamer elution from the gel filtration column in Supplementary Fig. S3A was examined with SDS-PAGE. D) DNA gel electrophoresis shows the shift band of the assembled nucleosome compared with free DNA. E) EMSA shows the binding ability of N protein to assembled nucleosomal DNA.