The incorporation of uracil into animal cell DNA in vitro

In the presence of dUTP, net DNA synthesis in vitro is substantially reduced. Small DNA fragments that arise during in vitro DNA synthesis in the presence of dUTP are produced as a result of dUMP incorporation and subsequent post-replication excision repair process initiated by uracil-DNA-glycosylase. The size of the fragments is dependent upon the amount of dUMP incorporated, but unlike the normal 4S intermediates of DNA synthesis, these repair products are not precursors to high molecular weight DNA but are further degraded. The high levels of dUTPase as well as the presence of RNA primers on most nascent DNA pieces (Tseng and Goulian, 1977) suggest that repair of uracil-containing DNA does not contribute to the generation of the small, nascent DNA pieces found during DNA synthesis in this in vitro system.