Zaman Sephorah, Fitzpatrick Megan, Lindahl Lasse, Zengel Janice
Department of Biological Sciences, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA.
Mol Microbiol. 2007 Nov;66(4):1039-50. doi: 10.1111/j.1365-2958.2007.05975.x. Epub 2007 Oct 22.
L4 and L22, proteins of the large ribosomal subunit, contain globular surface domains and elongated 'tentacles' that reach into the core of the large subunit to form part of the lining of the peptide exit tunnel. Mutations in the tentacles of L4 and L22 confer macrolide resistance in a variety of pathogenic and non-pathogenic bacteria. In Escherichia coli, a Lys-to-Glu mutation in L4 and a three-amino-acid deletion in the L22 had been reported. To learn more about the roles of the tentacles in ribosome assembly and function, we isolated additional erythromycin-resistant E. coli mutants. Eight new mutations mapped in L4, all within the tentacle. Two new mutations were identified in L22; one mapped outside the tentacle. Insertion mutations were found in both genes. All of the mutants grew slower than the parent, and they all showed reduced in vivo rates of peptide-chain elongation and increased levels of precursor 23S rRNA. Large insertions in L4 and L22 resulted in very slow growth and accumulation of abnormal ribosomal subunits. Our results highlight the important role of L4 and L22 in ribosome function and assembly, and indicate that a variety of changes in these proteins can mediate macrolide resistance.
L4和L22是大核糖体亚基的蛋白质，它们含有球状表面结构域和伸向大核糖体亚基核心的细长“触角”，形成肽出口通道内衬的一部分。L4和L22触角中的突变在多种致病和非致病细菌中赋予大环内酯抗性。在大肠杆菌中，已报道L4中有一个赖氨酸到谷氨酸的突变以及L22中有一个三个氨基酸的缺失。为了更多地了解触角在核糖体组装和功能中的作用，我们分离了其他耐红霉素的大肠杆菌突变体。八个新突变定位在L4中，均在触角内。在L22中鉴定出两个新突变；一个定位在触角外。在两个基因中都发现了插入突变。所有突变体的生长都比亲本慢，并且它们都显示出体内肽链延伸速率降低和前体23S rRNA水平升高。L4和L22中的大插入导致生长非常缓慢和异常核糖体亚基的积累。我们的结果突出了L4和L22在核糖体功能和组装中的重要作用，并表明这些蛋白质中的多种变化可以介导大环内酯抗性。
