Labeled DNA fibers used in this study (IMAGE) National Institutes of Natural Sciences Caption In the DNA fiber assay used in this study, cells labeled with IdU (green) and CldU (red) nucleotide analogs were sorted into substages of S phase before being subjected to the DNA fiber assay. This method allows for the measurement of various parameters, such as replication fork speed, fork pausing rate, and origin-firing rate in substages of S phase. Credit K. Kurashima Usage Restrictions For use in stories about this research. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.