DNA single-strand breaks in adult and embryonic avian erythrocytes

We have investigated the possibility that the reactivation rate of adult avian erythrocytes, which is slower than that of embryonic erythrocytes, after fusion with metabolically active cells, is due to a greater number of single-strand breaks (ssb) in the DNA of the former. We have assayed ssb by measuring the template activity of the erythrocyte nuclei for added Escherichia coli DNA polymerase. We have found that differences in the numbers of ssb within polymerase-accessible regions between adult and embryonic cells are within experimental error. We conclude that, unless very localized clusters of damage exist within the DNA (which would not be detectable by this or other techniques), the difference in reactivation rate is not attributable to differences in ssb numbers.