Genomic recombination upon transduction of CPP-Cre conjugates in reporter cells. (A) Peptidic additions to Cre recombinase: 'NLS', nuclear localization signal; '3' or 'Penetratin', Antennapedia transduction domain, see ; '23' or 'SEC', Antennapedia secretion signal, see ; 'TAT', transduction domain from HIV Tat protein (see ); 'myc', myc tag; 'his', polyhistidine tag. See also Additional file 1. (B) β-Galactosidase activity (arrow) of CV-1B reporter cells following 1 h incubation with H3C. Arrows, pairs of daughter cells from individually transduced cells. (C) Bradford quantification of total protein content after conjugate exposure showed unaffected cellular survival upon transduction. MTT cell viability assays on the same samples indicated that conjugate doses only above 5 μM were cytotoxic (not shown). (D) Dose-dependent transduction assay. Reporter activity was quantified 48 h after 1 h exposure to conjugates. The indicated proteins showed strongest activity at 4 μM, with a maximum for H3C. H3NC reached similar levels (see Additional file 2D). Scale bar in B represents 1800 μm.