The roles of proteins L28 and L33 in the assembly and function of Escherichia coli ribosomes in vivo

Abstract

SummaryStrain BM108 of Escherichia coli has a chromosomal mutation in the rpmB,G operon that prevents synthesis of ribosomal proteins L28 and L33. The mutation was lethal unless synthesis of protein L28 was induced from a plasmid. Without protein L28, RNA and protein synthesis were linear rather than exponential. No 70S ribosomes were made. Instead, RNA accumulated in '30S material' and '47S particles'; the latter were distinct from 50S ribosomal subunits, lacked proteins L28 and L33 and had substoicheometric amounts of three other proteins. When L28 synthesis was induced (but protein L33 was still absent), the strain grew as well as, and assembled 70S ribosomes with similar kinetics to, a wild-type control. Thus, protein L28 is required for ribosome assembly in strain BM108 while protein L33 has no significant effect on ribosome synthesis or function.

Rpl33, a Nonessential Plastid-Encoded Ribosomal Protein in Tobacco, Is Required under Cold Stress Conditions

“…The only experimental condition that elicited a strong phenotypic effect was chilling stress at 48C, suggesting that the lack of the chloroplast L33 protein renders plants sensitive to chilling. It is noteworthy in this respect that rpl33 loss-of-function mutants found in E. coli (Sims and Wild, 1976;Butler and Wild, 1984;Maguire and Wild, 1997) also displayed a cold-sensitive phenotype (Dabbs, 1991), suggesting that the cold stress-related function of L33 in translation has been evolutionarily conserved. However, E. coli rpl33 null mutants showed no measurable effect on translation in cells growing exponentially under normal conditions (Sims and Wild, 1976;Butler and Wild, 1984;Maguire and Wild, 1997), which is different from the situation in plants, where young expanding leaves show slightly reduced protein synthesis rates, as evidenced by a slightly delayed biogenesis of the photosynthetic complexes (Table 1).…”

Synthetic Lethality in the Tobacco Plastid Ribosome and Its Rescue at Elevated Growth Temperatures

“…The genes for the Rps15 protein (S15) of the small ribosomal subunit and the Rpl33 (L33) and Rpl36 (L36) proteins of the large ribosomal subunit can be inactivated in E. coli (Maguire and Wild, 1997;Ikegami et al, 2005;Ikegami et al, 2005) and in plastids (Rogalski et al, 2008;Fleischmann et al, 2011) without losing viability. While the rpl36 gene knockout in tobacco (Nicotiana tabacum) plastids displays a severe mutant phenotype, rpl33 and rps15 knockout plants are nearly indistinguishable from the wild type (Rogalski et al, 2008;Fleischmann et al, 2011).…”

Inhibition of Bacterial Ribosome Assembly: a Suitable Drug Target?

“…An example is provided by the conditional repression of synthesis of proteins L28 and L33 in vivo. Assembly of the 50S subunit ceases abruptly when these proteins are no longer made (106), and an abnormal precursor accumulates instead. Growth is limited by the existing ribosome concentration and so is arithmetic rather than logarithmic (Fig.…”

“…However, they all cluster around protein L15 in the in vitro assembly map, and therefore, the assembly of this group may be more cooperative in vivo than in vitro. Although neither L28 nor L33 was ascribed an important role in vitro, if both are absent, no 50S subunits are made in vivo (106).…”