Saccharomyces cerevisiae strain PSY2088 (MAT rpl11a::HIS3 rpl11b::HIS3 ura3-52 leu2D1 trp1D63 his3D200 + YCpL11B URA3), an rpl11a/rpl11b gene deletion strain in which L11 is supplied by a URA3-CEN6 based RPL11B clone, was a generous gift from Dr. Pamela Silver (21) . The L-A and M 1 viruses were introduced into PSY2088 by cytoplasmic mixing (cytoduction) through nonproductive mating with JD758 [MATa kar1-1 arg1 (L-AHN M 1 )] to produce the Killer + strain JD1313 as previously described (19) . Wild-type RPL11B was isolated from yeast strain PSY2088 plasmid (pYCP50L11B URA3). Using flanking BamHI restriction sites, a 2.2-kb fragment of DNA containing both the 525-bp wild-type RPLL11B ORF plus the native 5 0 and 3 0 UTR regions (1228 bp and 485 bp, respectively) was purified by agarose gel electrophoresis. This 2238-bp fragment was ligated into BamHI digested pRS314, a low copy TRP1-selectable plasmid (purchased from ATCC, Manassas, VA, USA) (22) to create pRS314L11B-TRP1. This plasmid served as the template for generation of rpl11B mutants by site directed mutagenesis using the primers listed in Supplementary  Table S1 . Wild-type and mutant pRS314L11B-TRP1 clones were transformed into JD1313, selected for growth on -trp medium, and cells having lost the URA3-based plasmid were identified by their ability to grow in the presence of 5-fluoroorotic acid (5-FOA) (23) .