ILLEGITIMATE RECOMBINATION IN XENOPUS - CHARACTERIZATION OF END-JOINED JUNCTIONS

When linear DNAs are injected into Xenopus laevis eggs, they are conve rted into several different kinds of recombination products. Some mole cules undergo homologous recombination by a resection-annealing mechan ism; some ends are precisely ligated; and some ends are joined by ille gitimate means. The homologous and illegitimate products are also gene rated in nuclear extracts from stage VI Xenopus oocytes. In order to g ain insight into the mechanism(s) of illegitimate end joining, we ampl ified, cloned and sequenced a number of junctions from eggs and from o ocyte extracts. The egg junctions fell into three categories: some wit h no homology at the join point that may have been produced by blunt-e nd ligation; some based on small, but significant homologies (5-10 bp) ; and some with matches of only 1 or 2 nucleotides at the joint. Junct ions made in oocyte extracts were largely of the latter type. In the e xtracts, formation of illegitimate joints required the addition of all four deoxyribonucleoside triphosphates and was inhibited by aphidicol in. This indicates that this process involves DNA synthesis, and mecha nisms incorporating this feature are considered. The spectrum of recom bination products formed in Xenopus eggs is very reminiscent of those produced from DNA introduced into mammalian cells.