Fig. 6. Lack of evidence for chromosomal end-to-end fusions as the source of the long TRFs. (A) Time course of Bal31 exonuclease digestion of genomic DNA from HUVEC of the indicated replicative ages and culture conditions. Southern blot analysis for mean TRF length determination was performed as described in Fig. 4. The three lanes for each treatment are from samples digested with Bal31 for 30, 60 and 120 minutes, respectively. (B) The mean TRF length is plotted against the time of Bal31 digestion.