A core activity associated with the N terminus of the yeast RAD52 protein is revealed by RAD51 overexpression suppression of C-terminal rad52 truncation alleles.

C-terminal rad52 truncation and internal deletion mutants were characterized for their ability to repair MMS-induced double-strand breaks and to produce viable spores during meiosis. The rad52-Delta251 allele, encoding the N-terminal 251 amino acids of the predicted 504-amino-acid polypeptide, supports partial activity for both functions. Furthermore, RAD51 overexpression completely suppresses the MMS sensitivity of a rad52-Delta251 mutant. The absence of the C terminus in the truncated protein makes it likely that suppression occurs by bypassing the C-terminal functions of Rad52p. RAD51 overexpression does not suppress the low level of spore viability that the rad52-Delta251 allele causes and only partially suppresses the defect in rad52 alleles encoding the N-terminal 292 or 327 amino acids. The results of this study also show that intragenic complementation between rad52 alleles is governed by a complex relationship that depends heavily on the two alleles involved and their relative dosage. In heteroallelic rad52 diploids, the rad52-Delta251 allele does not complement rad52 missense mutations altering residues 61 or 64 in the N terminus. However, complementation is achieved with each of these missense alleles when the rad52-Delta251 allele is overexpressed. Complementation also occurs between rad52-Delta327 and an internal deletion allele missing residues 210 through 327. We suggest that the first 251 amino acids of Rad52p constitute a core domain that provides critical RAD52 activities.