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Abstract 1 of 1Mol Cell Biol. 1993 November; 13(11): 6897-6906
C W Lehman, M Clemens, D K Worthylake, J K Trautman, and D Carroll
Department of Biochemistry, University of Utah School of Medicine, Salt Lake City 84132.
Exogenous DNA is efficiently recombined when injected into thenuclei of Xenopus laevis oocytes. This reaction proceeds bya homologous resection-annealing mechanism which depends onthe activity of a 5'-->3' exonuclease. Two possible functionsfor this recombination activity have been proposed: it may bea remnant of an early process in oogenesis, such as meioticrecombination or amplification of genes coding for rRNA, orit may reflect materials stored for embryogenesis. To test thesehypotheses, recombination capabilities were examined with oocytesat various developmental stages. Late-stage oocytes performedonly homologous recombination, whereas the smallest oocytesligated the restriction ends of the injected DNA but supportedno homologous recombination. This transition from ligation torecombination activity was also seen in nuclear extracts fromthese same stages. Exonuclease activity was measured in thenuclear extracts and found to be low in early stages and thento increase in parallel with recombination capacity in laterstages. The accumulation of exonuclease and recombination activitiesduring oogenesis suggests that they are stored for embryogenesisand are not present for oocyte-specific functions. Eggs werealso tested and found to catalyze homologous recombination,ligation, and illegitimate recombination. Retention of homologousrecombination in eggs is consistent with an embryonic functionfor the resection-annealing mechanism. The observation of allthree reactions in eggs suggests that multiple pathways areavailable for the repair of double-strand breaks during theextremely rapid cleavage stages after fertilization.
Mol Cell Biol. 1993 November; 13(11): 6897-6906