Figure 3.

Super-infection of ES cells by co-cultivation. (a) Efficiency of infection by co-cultivation with the viral producer cell line B4-5. AB2.2, wild-type (WT), and NGG5.3 Blm-deficient embryonic stem cells cells were co-cultivated with irradiated B4-5 cells and plated in normal medium to determine plating efficiency in the absence of selection and 1-(-2-deoxy-2-fluoro-1-β-D-arabino-furanosyl)-5-iodouracil (FIAU) to measure the frequency of noninfected cells. (b) Assessment of proviral copy number in randomly picked nonselected wild-type and Blm-deficient embryonic stem (ES) cells after co-cultivation with the viral producer cell line B4-5. Southern blot analysis was performed by using HindIII digested genomic DNA isolated from different single cell clones cultured in nonselective medium. Each observed fragment represents a different proviral insertion. The probe is the PstI fragment generated from Puro-Δk cassette. kb, kilobases; LTR, long terminal repeat.