An extensive mutational analysis of RPL33A, encoding the yeast ribosomal protein L33A (eL33) allowed us to identify several novel rpl33a mutants with different translational phenotypes. Most of the rpl33a mutants are defective in the processing of 35S and 27S pre-rRNA precursors and the production of mature rRNAs, exhibiting reductions in the amounts of ribosomal subunits and altered polysome profiles. Some of the rpl33a mutants exhibit a Gcd⁻ phenotype of constitutive derepression of GCN4 translation and strong slow growth phenotypes at several temperatures. Interestingly, some of the later mutants also show a detectable increase in the UUG/AUG translation initiation ratio that can be suppressed by eIF1 overexpression, suggesting a requirement for eL33 and a correct 60S/40S subunit ratio for the proper recognition of the AUG start codon. In addition to producing differential reductions in the rates of pre-rRNA maturation and perhaps in r-protein assembly, most of the point rpl33a mutations alter specific molecular interactions of eL33 with the rRNAs and other r-proteins in the 60S structure. Thus, rpl33a mutations cause distinctive effects on the abundance and/or functionality of 60S subunits, leading to more or less pronounced defects in the rates and fidelity of mRNA translation.

对编码酵母核糖体蛋白 L33A (eL33)的RPL33A进行广泛的突变分析，使我们能够识别出几种具有不同翻译表型的新型rpl33a突变体。大多数rpl33a突变体在 35S 和 27S pre-rRNA 前体的加工和成熟 rRNA 的产生方面存在缺陷，表现出核糖体亚基数量的减少和多核糖体谱的改变。一些rpl33a突变体表现出 Gcd ^- GCN4组成型去阻遏的表型在几个温度下翻译和强烈的缓慢生长表型。有趣的是，一些后来的突变体也显示出 UUG/AUG 翻译起始比率的可检测增加，这可以被 eIF1 过表达抑制，表明需要 eL33 和正确的 60S/40S 亚基比率才能正确识别 AUG 起始密码子. 除了在前 rRNA 成熟率和可能在 r 蛋白组装中产生不同的降低外，大多数点rpl33a突变改变了 eL33 与 60S 结构中的 rRNA 和其他 r 蛋白的特定分子相互作用。因此，rpl33a突变会对 60S 亚基的丰度和/或功能产生显着影响，导致 mRNA 翻译的速率和保真度出现或多或少明显的缺陷。