Figure 8.

Multiple copies of the ubi3ΔN-HA allele partially alleviate the growth and ribosome biogenesis defects linked to a sole genomic copy of this allele. (A) Growth test of mutants harbouring single or multiple copies of the ubi3ΔN-HA allele. Strains TLY56.D3 and TLY63.A3, which harbour genomically integrated UBI3-HA and ubi3ΔN-HA constructs at the UBI3 locus, respectively, were transformed with the empty high-copy-number plasmid YEplac181. The ubi3 null mutant (ubi3Δ) strain TLY12.1A was transformed with the high-copy-number plasmids YEplac181-UBI3-HA or YEplac181-ubi3ΔN-HA. Transformants were grown in liquid SD-Leu medium and diluted to an OD₆₀₀ of 0.05. Serial 5-fold dilutions were spotted onto SD-Leu plates, which were incubated at either at 30°C or 22°C for 3 and 5 days, respectively. (B) Overexpression of the S31ΔN protein leads to nearly wild-type polysome profiles. The indicated strains were grown in SD-Leu medium at 22°C to mid-log phase. Cell extracts were prepared and 10 A₂₆₀ units of each cell extracts were resolved in 7–50% sucrose gradients. The A₂₅₄ was continuously measured. Sedimentation is from left to right. The peaks of free 40S and 60S r-subunits, 80S vacant ribosomes/monosomes and polysomes are indicated.