FIG. 3.

Complementation analysis. The unmodified REF2 proteins shown in (A) were expressed in a Δref2 strain from a low-copy plasmid under the control of the natural REF2 promoter. YCplac33 represents the parental vector into which the various mutated REF2 genes were inserted. The truncated protein REF2345 represents the gene product of the ref2-1 allele, which was originally identified in a selection for Hol⁺ phenotypes (45). Transformed strains were tested (B) for their ability to grow at 37°C or on medium containing histidinol in place of histidine (see text) and results are depicted on the right. In the case of growth at 37 °C, + + denotes wild-type growth, – indicates slight growth as observed for the Δref2 strain, whereas + represents an intermediate phenotype.