Est1 hybrids do not rescue est1Δ rad52Δ strains or interfere with growth of rad52Δ strains. (A) Heterozygous diploid est1Δ rad52Δ yeast were transformed with pRS316(URA3) or pRS426(URA3) plasmids alone ('vector') or plasmids expressing yeast/human EST1 hybrids in which the TPR of ScEst1 was replaced with the TPR of hEST1A/B/C, or GFP(S65T). Haploid spores were isolated and passaged every two days on plates containing synthetic dropout media lacking uracil. Summary plates of growth from the 1st passage to 6th passage (as shown, counter-clockwise) were prepared by re-streaking colonies from each passage onto one sector of a single plate (refer to Methods). Refer to Additional file 1, Figure S4 for summary of spore growth. (B, C) Yeast/human Est1 hybrid proteins were expressed. Western blot of cell lysates using anti-FLAG and anti-mouse IgG-HRP antibodies. Arrowheads indicate wild-type or hybrid Est1 proteins. A non-specific, cross-reacting band is indicated with an asterisk (*). Molecular mass (kDa) is indicated at the left.