Figure 8.

Human fibroblasts delete unpaired DNA loops, but do not cause measurable expansions or contractions of DNA stem–loops. These gels show the length of DNA bands after strand specific PCR of vector controls and DNA recovered from normal primary fibroblasts. Lane (a) is strand specific PCR of control vector pW-GR. Lane (b) is strand specific PCR the respective expanded or deleted control vector. Lane (c) is strand specific PCR of the experimental vector prior to introduction to cells. Although only one band should be present in this lane, there was a faint second band limiting the sensitivity of the assay due to difficulty removing 100% of the linear extension primer prior to PCR. Leftover extension primer caused some amplification of the opposite strand in heteroduplex vectors. Significant expansions or deletions were measured as signal above this background. Lane (d) is strand specific PCR of the experimental vector after recovery from normal primary fibroblasts. Open arrowheads indicate bands with an equal representation in control and experimental samples. Filled red arrowheads indicate bands where there was a significant difference (P< 0.05) in the experimental samples. Statistical tests were performed by one-way analysis of variance with contrasts to delineate specific comparisons. Gels were cropped and ordered for clarity, maintaining their relationship to the marker. Brightness and contrast were adjusted as needed to allow visualization of DNA bands.