CarD integrates three functional modules to promote efficient transcription, antibiotic tolerance, and pathogenesis...

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Prokaryotic transcription requires additional factors for efficiency in some bacteria.
• CarD is a conserved RNA polymerase (RNAP)-binding protein essential in mycobacteria, but its precise function remains unclear.

Purpose of the Study:

• To dissect the functional roles of CarD's distinct modules in transcriptional regulation.
• To elucidate CarD's contribution to stabilizing RNAP-promoter complexes.
• To investigate CarD's differential requirements and functions in Mycobacterium tuberculosis versus Mycobacterium smegmatis.

Main Methods:

• Site-directed mutagenesis targeting three functional modules of CarD: RNAP interaction domain, DNA-binding domain, and a conserved tryptophan residue.
• Analysis of CarD mutant activities in transcription complexes.
• Comparative studies in Mycobacterium tuberculosis and Mycobacterium smegmatis.

Main Results:

• All three functional modules of CarD are required for its activity in Mycobacterium tuberculosis, but not in Mycobacterium smegmatis.
• Each module contributes to stabilizing RNAP-promoter complexes, forming a model for CarD function.
• Divergent utilization of CarD functional modules was observed in resisting oxidative stress and in pigmentation.

Conclusions:

• The study provides a model for CarD function, highlighting the importance of its distinct modules in stabilizing transcription initiation complexes.
• Differential requirements for CarD modules in M. tuberculosis and M. smegmatis suggest species-specific roles in gene regulation.
• CarD's functional domains play varied roles in bacterial physiology, including stress response and pigmentation, particularly in M. tuberculosis.