Biology subjects

Polgar, P.

Publications and source records attributed to Polgar, P..

3 recordsLinked to original sources

bioRxiv2024

The RpfB switch is a novel B12-sensing riboswitch regulating (non-replicating) persistence in Mycobacterium tuberculosis.

Riboswitches are metabolite-sensing RNA elements that control a wide range of genes in bacteria. Most riboswitches identified to date are broadly conserved and control genes that are directly involved in the transport or biosynthesis of their cognate ligands. However, a minority of switches are restricted to a few species and in addition may bind less obvious ligands. One such switch controls the expression of the Mycobacterium tuberculosis rpfB operon, which is critical for resuscitation of dormant bacteria, ribosome maturation and reactivation of latent tuberculosis infection. The switch is restricted to pathogenic mycobacteria and until now, its ligand was unknown. However, in the current study, we identify the ligand as cobalamin or vitamin B12. Using in-line probing, we show that vitamin B12 binds directly to the riboswitch RNA, and we predict a structure based on the cleavage pattern. Moreover, we show that B12 suppresses the expression of an rpfB-lacZ reporter fusion and crucially, that B12 suppresses resuscitation of M. tuberculosis from a state of non-replicating persistence. These findings demonstrate a pivotal role of crosstalk between a host-derived metabolite and a pathogen riboswitch in controlling M. tuberculosis persistence with potential for improved interventions.

molecular biology↗

bioRxiv2023

Mycobacterium tuberculosis employs atypical and different classes of B12 switches to control separate operons

Vitamin B12 (B12), an essential cofactor in all domains of life, is produced de novo by only a small subset of prokaryotes, but B12-sensing riboswitches are some of the most widely distributed riboswitches in bacteria. Mycobacterium tuberculosis, the causative agent of the ongoing tuberculosis pandemic, encodes two distinct vitamin B12 riboswitches. One controls the expression of metE, encoding a B12-independent methionine synthase, while the other is located upstream of ppe2, a PE/PPE family gene whose function is still unresolved. Here, we analyse ligand sensing, secondary structure architecture, and gene expression control mechanisms of these two riboswitches. Our results provide the first evidence of direct ligand binding by metE and ppe2 riboswitches and show that the two switches exhibit different preferences for natural isoforms of B12, use distinct regulatory and structural elements, and act as translational OFF switches. Based on our results, we propose that the ppe2 switch represents a new Class IIc of B12-sensing riboswitches. Moreover, we have identified small translated open reading frames (uORFs) upstream of both metE and ppe2, which modulate the expression of the respective downstream genes in opposite directions. Translation of the metE riboswitch uORF suppresses MetE expression, while translation of the uORF in the ppe2 switch is essential for PPE2 expression via the synthesis of a uORF-PPE2 fusion protein. In summary, our findings reveal an unexpected diversity and complexity of B12-dependent cis-regulation in M. tuberculosis, with potential implications for host-pathogen interactions.

molecular biology↗

bioRxiv2022

Term-seq reveals an abundance of conditional, Rho-dependent termination in Mycobacterium tuberculosis.

Little is known about the decisions behind transcription elongation versus termination in the human pathogen Mycobacterium tuberculosis. By applying Term-seq to M. tuberculosis we found that the majority of transcription termination is premature and associated with translated regions, i.e. within previously annotated or newly identified open reading frames. Computational predictions and Term-seq analysis upon depletion of termination factor Rho suggests that Rho-dependent transcription termination dominates all TTS including those associated with regulatory 5 leaders. Moreover, our results suggest that tightly coupled translation, in the form of overlapping stop and start codons, may suppress Rho-dependent termination. This study provides detailed insights into novel M. tuberculosis cis-regulatory elements, where Rho-dependent, conditional termination of transcription and translational coupling together play major roles in gene expression control. Our findings contribute to a deeper understanding of the fundamental regulatory mechanisms that enable M. tuberculosis adaptation to the host environment offering novel potential points of intervention.

microbiology↗