The tNTS confers tumour cell selectivity to core histone variants. A. Schematic representation of the engineered histone H2B and H3 proteins utilised in this study. GFP, Green Fluorescent Protein; H2B, histone H2B; H3, histone H3; Op-T-NLS, optimised NLS from the SV40 large tumour antigen (T-ag); tNTS, C-terminal domain of Apoptin (aa 74–121). B. SR5 (normal) or SAOS-2 (tumour) cells were transfected to express the indicated fusion proteins followed by CLSM analysis 6 h post-transfection. C. Analysis of digitised images such as those shown in B was used to determine the relative levels of nuclear accumulation as described in materials and methods. Results represent the mean Fn/c ± SEM (n > 10) and p values indicate significant differences as determined by the students t-test. D. Cancer comparative indexes (CCI) of the results shown in C, determined from a ratio of the Fn/c values. E. SR40 (normal) or SAOS-2 (tumour) cells were transfected to express the indicated fusion proteins and imaged by CLSM 6 h post-transfection. F. Images such as those in E were analysed as per C to determine the Fn/c ratio. G. CCI’s calculated as per D from the results in F.