Function of the Synechocystis RNA helicase, CrhR, and its cyanobacterial homologs

  • Author / Creator
    Whitford, Denise Samantha
  • RNA helicases function in all aspects of RNA metabolism, regulating a diverse range of cellular processes by rearranging RNA structures and mediating RNA-protein interactions. Prokaryotic RNA helicases have been shown to have roles in RNA degradation, ribosome biogenesis and translation, with their effects on these processes enhanced during abiotic stress. The model cyanobacterium Synechocystis sp. PCC 6803 encodes a single DEAD-box RNA helicase, CrhR. CrhR expression is known to be regulated by a variety of abiotic stresses, sensed through the redox poise of the photosynthetic electron transport chain; however, the cellular role of CrhR is unknown.
    Evidence is presented that is consistent with CrhR performing roles in translation and RNA processing/degradation. CrhR co-precipitates with actively translating polysomes and components of the RNA degradosome, an interaction that is RNA-dependent. CrhR was also found to localize to the thylakoid membrane space in Synechocystis. The helicase also enhances processing of its own dicistronic transcript, at a site with sequence and structural features sufficient for cleavage by recombinant RNase E in vitro. CrhR participation in translation and RNA processing/degradation, combined with prior transcriptomic and proteomic studies, suggest CrhR regulates expression of genes involved in photosynthesis, energy metabolism, carbon metabolism, and protein stability and turnover. Related to these crucial metabolic pathways, it is shown that CrhR is regulated in response to nitrogen availability. Similar to other abiotic stresses, crhR mutation affects growth rate and abundance of photosynthetic pigments differentially in response to various sources of fixed nitrogen. Cyanobacterial nitrogen metabolism is interconnected with photosynthetic energy transfer, enhanced reduction of which regulates CrhR expression. This links the role of CrhR during nitrogen stress with the other characterized abiotic stresses that are sensed through the redox poise of the photosynthetic electron transport chain.
    Conservation of CrhR throughout the majority of cyanobacterial diversity was also shown. These CrhR-like helicases form a separate clade, defined by a characteristic highly conserved sequence motif in the C-terminus that is unique to cyanobacterial DEAD-box proteins. It is believed that this motif may function in substrate specificity or auto-regulation of CrhR abundance.
    In this thesis, a function for CrhR in regulating maintenance of photosynthesis and thylakoid membranes, particularly energy transfer, through the effects of CrhR on RNA maturation, stability and translation is proposed. This function, unique to cyanobacterial DEAD-box RNA helicases, appears to be conserved throughout cyanobacteria that encode CrhR-like helicases.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
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