Abstract
The BipA (BPI-inducible protein A) protein is highly conserved in a large variety of bacteria and belongs to the translational GTPases, based on sequential and structural similarities. Despite its conservation in bacteria, bipA is not essential for cell growth under normal growth conditions. However, at 20°C, deletion of bipA causes not only severe growth defects but also several phenotypic changes such as capsule production, motility, and ribosome assembly, indicating that it has global regulatory properties. Our recent studies revealed that BipA is a novel ribosome-associating GTPase, whose expression is cold-shock-inducible and involved in the incorporation of the ribosomal protein (r-protein) L6. However, the precise mechanism of BipA in 50S ribosomal subunit assembly is not completely understood. In this study, to demonstrate the role of BipA in the 50S ribosomal subunit and possibly to find an interplaying partner(s), a genomic library was constructed and suppressor screening was conducted. Through screening, we found a suppressor gene, rplT, encoding r-protein L20, which is assembled at the early stage of ribosome assembly and negatively regulates its own expression at the translational level. We demonstrated that the exogenous expression of rplT restored the growth of bipA-deleted strain at low temperature by partially recovering the defects in ribosomal RNA processing and ribosome assembly. Our findings suggest that the function of BipA is pivotal for 50S ribosomal subunit biogenesis at a low temperature and imply that BipA and L20 may exert coordinated actions for proper ribosome assembly under cold-shock conditions.
Highlights
IntroductionRibosome biogenesis is a highly complex process with chains of events including transcription, processing, and modifications of ribosomal RNAs (rRNAs) and ribosomal proteins (r-proteins), and the assembly of dozens of r-proteins with rRNAs (Wimberly et al, 2000)
Ribosome biogenesis is a highly complex process with chains of events including transcription, processing, and modifications of ribosomal RNAs and ribosomal proteins (r-proteins), and the assembly of dozens of r-proteins with rRNAs (Wimberly et al, 2000)
In an attempt to further comprehend the function of BipA in E. coli, we constructed a genomic library and searched for an element(s) in the E. coli genome that can recover the growth defect of strain ESC19 at low temperature
Summary
Ribosome biogenesis is a highly complex process with chains of events including transcription, processing, and modifications of ribosomal RNAs (rRNAs) and ribosomal proteins (r-proteins), and the assembly of dozens of r-proteins with rRNAs (Wimberly et al, 2000). Deletion of bipA affects pathogenicity, regulation of capsule synthesis, and flagella-mediated motility, suggesting that BipA may function as a regulator of a variety of virulence factors (Farris et al, 1998; Rowe et al, 2000; Grant et al, 2003; Duo et al, 2008). In both pathogenic and non-pathogenic bacteria, BipA is implicated in resistance to other stress factors such as antimicrobial peptides, antibiotics, acidic conditions, and detergent stress (Qi et al, 1995; Farris et al, 1998; Kiss et al, 2004; Duo et al, 2008; Neidig et al, 2013). Even in chloroplasts of S. salsa, the expression of bipA is upregulated by a variety of external stressors, and BipA plays an important role in obtaining tolerance to oxidative stresses (Wang et al, 2008)
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