INFLUENCE OF NON-HOMOLOGY BETWEEN RECOMBINING DNA-SEQUENCES ON DOUBLE-STRAND BREAK REPAIR IN SACCHAROMYCES-CEREVISIAE

In this paper we study the influence of nonhomology between plasmid an d chromosomal DNA on the efficiency of recombinational repair of plasm id double-strand breaks and gaps in yeast. For this purpose we used di fferent combinations of plasmids and yeast strains carrying various de letions within the yeast LYS2 gene. A 400 bp deletion in plasmid DNA h ad no effect on recombinational plasmid repair. However, a 400 bp dele tion in chromosomal DNA dramatically reduced the efficiency of this re pair mechanism, but recombinational repair of plasmids linearized by a double-strand break with cohesive ends still remained the dominant re pair process. We have also studied the competition between recombinati on and ligation in the repair of linearized plasmids. Our experimental evidence suggests that recombinational repair is attempted but aborte d if only one recombinogenic end with homology to chromosomal DNA is p resent in plasmid DNA. This situation results in a decreased probabili ty of non-recombinational (i.e, ligation) repair of linearized plasmid DNA.