Ghapter 18 Antisense Effec"ts of PIIAs in Bacteria Shan Goh, Jem Stach, and Liam Good Key words Peptide nucleic acid (PNA), DNA analogue, Solid-phase peptide synthesis (SPPS), Metal complexes, Click chemistry 1 lntroduction l.l llative Antisense in Bacteria Antisense peptide nucleic acid (PNA) can enter bacteria and con- uol gene expression through targeted RNA silencing. Bacterial cell barriers pose a formidable challenge to achieving efficient synthetic antisense effecs. Fortunatelg PNAs can be attached to cell wall active peptides to confer improved uptake and antisense ProPer- ties. Antisense PNfu provide an alternative approach to control bacterial gene expression for gene functional studies and anti- infectives development, using protocols described in this chapter. RNA silencing is widespread in nature. The transcripts involved are often termed noncoding regulatory RNAS or antisense RNA, and there are a range ofmechanisms and cellular roles described [I]. These natural examples of RNA silencing provide important infor- mation about how synthetic RNA strategies can be best developed in practice. It is easy to envision how this can occur in bacteria, whire the ribosome binds to mRNA at the well-characterized ribosome-binding site (RBS) (Shine and Dalgarno L974). Peter E. Nielsen and Daniel H. App€lla (eds.), Peptide Nucleic Acids: Methods and Protocols, Methods in Molecular Biology, vol. 1050, DOI 10.1007/978-1-62703-553-8-18, @ Springer Science+Business Media New York 2014 223