Fig. 2.

UBI4 repeat number influences survival after heat shock in natural and engineered Saccharomyces strains. a Survival of 65 diverse Saccharomyces strains after heat shock (43 °C, 4 h) is influenced by the number of ubiquitin units in their UBI4 gene, and not their industrial niches (right panel). The strains designated as having a UBI4 gene of 4 or 5 repeats used in this experiment were all homozygous for the UBI4 gene; strains designated as having 2 or 3 UBI4 repeats were heterozygous for the UBI4 gene, with the other allele having 4 or more repeats. b Survival levels of haploid derivatives of industrial and feral S. cerevisiae strains increase with their UBI4 repeat number. It should be noted that no haploid strains with a repeat number over 5 were available. c Survival after heat shock (44 °C, 4 h) of haploid isogenic S. cerevisiae S288c variants containing different numbers of UBI4 repeats. The scheme shows the UBI4 gene structure in these repeat variants. Data points represent mean ± SD; n = 3. d Heat shock survival of isogenic S. cerevisiae strains containing multiple copies of a mono-unit UBI4 gene (i.e., encoding only one ubiquitin unit) correlates with the total number of ubiquitin-coding units. The scheme shows the structure of the mono-ubiquitin copy number variants. The first two copies were inserted in tandem (at the UBI4 gene locus), whereas the third unit (depicted by the yellow overhangs) was inserted in a neutral genomic location. Data points represent mean ± SD; n = 4 or 6. Statistical significance was assessed using the Mann–Whitney test (a, b) or an unpaired t-test (with Welch’s correction) (c, d). NS, not significant (P > 0.05), *P < 0.05, **P < 0.01, ***P < 0.001. For the sake of clarity, only significant differences in survival are shown