The discontinuous DNA replication model proposed by Okazaki lends an explanation to the paradox that even though DNA replication takes place on both strands of a DNA duplex simultaneously at the same rate and in the same direction, there are no 3' yields 5' DNA polymerase. This model has been supported by the finding that pulse-labeled DNA in E. coli appears as DNA fragments of about 1000-2000 nucleotides. However, more recent studies on DNA fragments that arise from post-replication excision-repair of uracil shows that these repair products bear close-resemblance in pulse-labeling kinetics to the Okazaki fragments. Our objectives towards the understanding of DNA replication and repair in E. coli are: 1) To reexamine the origin(s) of Okazaki fragments in light of the excision-repair of uracil. 2) To exhaust other post-replication mechanisms that give rise to Okazaki fragments. 3) To study the effect of uracil substitution in DNA.