Table I.

Analysis of mean nuclear p53 immunofluorescence intensities in human/mouse heterokaryons

Irradiated cells	Treatment	p53 detected	Nuclei compared	p53 signal ratio	P-value
None	Untreated	Human	H inside/H outside	1.20	0.4567
			H inside/M inside	4.30	1.5 × 10−8
None	Untreated	Murine	M inside/M outside	2.83a	0.1962
			H inside/M inside	4.77	6.4 × 10−7
Murine	Untreated	Human	H inside/M inside	1.06	0.5735
Human	CHX	Human	H outside/H inside	2.16	0.0172
Human	MG132 + CHX	Human	H outside/H inside	1.34	0.0266
			H inside/M inside	1.02	0.9985
Human	LMB + CHX	Human	H outside/H inside	1.17	0.1491
			H inside/M inside	11.4	3.0 × 10−3

Human or murine p53 was detected with the species-specific mAbs DO-1 or PAb246, respectively. Inside and outside indicate being part or not of a heterokaryon, respectively, i.e., fused with a heterologous nucleus or not. p53 signal ratio indicates the average ratio of p53 mean intensities in each of the two types of nuclei compared. This value is only illustrative because the paired t test was used to establish the statistical difference between p53 mean intensities. P-value indicates the t test for the differences between the p53 nuclear fluorescence intensities under various conditions. Neighboring nuclei (both within and outside heterokaryons) from each field of view were compared. A paired t test was then applied to collate data from several fields. H, human; M, murine.

^aThis quantitation is unreliable because it corresponds to basal levels of murine p53 in 3T3 fibroblasts. Nevertheless, the p-value indicates that the presence of a nonstressed human nucleus in a heterokaryon does not significantly alter the p53 levels in the murine nucleus.