MB&B Special Seminar: Ailong Ke, “New Frontiers in CRISPR-Cas, beyond RNA-guided nucleases”

Event time: 
Thursday, March 30, 2023 - 4:00pm to 5:00pm
Bass Center for Molecular and Structural Biology (BASS) See map
266 Whitney Avenue
New Haven, CT 06511
Event description: 

Ailong Ke is a Professor in the Department of Molecular Biology and Genetics. Dr. Ke is a member of the Graduate Field of Biochemistry, Molecular and Cell Biology, the Graduate Field of Biophysics, and the Graduate Field of Chemistry and Chemical Biology. The Ke lab studies the structure and function of RNA molecules.
Research Focus:
1) CRISPR interference in Prokaryotes
The use of small RNAs to regulate gene expression is ubiquitous in all living organisms including bacteria. In one remarkable instance, bacteria and archaea acquire resistance to invading foreign nucleic acids - such as conjugative plasmids, transposable elements and phages - by employing an RNA-mediated defense mechanism. In this process, short fragments (~24 to 48 nucleotides) of the invading DNA are integrated in the genome as spacers between similarly sized clusters of regularly interspaced short palindromic repeats (CRISPRs). CRISPRs are a novel class of repetitive DNA that have been identified in 88% of the archaeal genomes and 39% of the bacterial genomes thus far sequenced, including important human pathogens such as Campylobacter jejuni, Clostridium botulinum, Listeria monocytogenes, Mycobacterium tuberculosis, Yersinia pestis, and enteropathogenic and enterohaemorrhagic Escherichia coli. Adjacent to the CRISPR repeats and spacers is a set of conserved CRISPR-associated (cas) genes that encode the Cas proteins. Owing to its widespread occurrence, the CRISPR defense system has attracted a great deal of attention.
2) Riboswitch
Riboswitches are structured RNAs that recognize specific small molecules, usually key metabolites inside the cell, and “switch” on or off gene expression at either transcription or translation level. The discovery of these short cis-acting RNA elements has drastically changed our understanding of gene regulation. Majority of riboswitches were found in prokaryotic genomes, while only a few examples of eukaryotic riboswitches have been reported. Riboswitches are especially prevalent in Gram-positive bacteria, exemplified by Bacillus subtilis as a model organism, but also in a number of important pathogens such as Bacillus anthracis, Staphylococcus, Enterococcus, Streptococcus, Listeria, Clostridium, and Mycobacterium. This and other characteristics attract increasing attention to target riboswitches for antibiotic development.
Of the twelve different riboswitch classes that recognize nine different key metabolites, S-adenosyl methionine (SAM) riboswitches are the most commonly found. For example, nearly half of all known riboswitches identified in B. anthracis bear consensus primary sequence and secondary structures of the S box motif. Three classes of SAM riboswitches have been found. They contain completely different secondary structures, representing nature’s three independent RNA solutions to achieve specific SAM recognition. We recently determined the crystal structures of two (out of three) SAM riboswitch classes: the E. faecalis SMK and the B. subtilis S-box.
3) Bacteriophage Phi29 Packaging RNA
How bacteriophage f29 packages its genome into protein capsids is a mystery and a marvel. The DNA genome is packed to near crystalline density inside the capsid, against internal pressure of up to 2000 psi, through a molecular motor composed of a dodecameric head-tail protein connector, and a pentameric prohead RNA (pRNA) and ATPase gp16. We are working on the structures of the packaging motor components to explain how this natural nano-machine works and why RNA is needed as a component.