Can RNA form base pairs? Yes, in many circumstances Some are strictly dsRNA molecules, others are folded back pieces of ssRNA with interactions between antiparallel and complementary residues Linked to the origin of life - folded RNA molecules can have enzymic function The issue is particularly relevant to new and exciting areas of biology

DNA vs RNA helices B-DNA A-RNA

Uracil is missing this!

Double stranded viral genomes Members of the Reoviridae (eg, Rotaviruses)

Single stranded RNA viral genomes Generally have a double stranded (ie, fully base paired) intermediate (for example the Picornaviridae - eg, poliovirus, rhinovirus) When in single stranded form there is extensive internal base pairing to generate complex 3D structures that have certain functions (eg, Internal ribosomal entry in picornaviruses)

Cap-dependent Cap-independent Stewart & Semler (1997) Sem Virol 8;242

Cap-dependent Cap-independent

What about ribosomal and transfer RNA?

tRNA (cont.) tRNA cloverleaf

Ribozymes “Hammerhead” RNA structures that catalyse RNA and DNA degradation Tom Cech - Nobel prize for his discovery Wayne Gerlach et al (CSIRO) - “gene shears” or targeted ribozymes RNA base pairing is central to their formation and functioning

Ribozyme structure

RNA interference (RNAi) Very hot topic in molecular biology Also known as “post-transcriptional gene silencing” Discovered in plants, known to also operate in fungi, worms, insects and even mammalian cells (in a modified form - see later) Ancient origin - probably confers resistance to some viruses, may also have a role in development

Mechanism of RNAi

RNAi as a research tool Rapid generation of “loss-of-function” mutants Cannot introduce long dsRNA into mammalian cells as this induces antiviral response Short interfering RNA (siRNA) is very effective Can be added exogenously or synthesised endogenously

Web sites of interest/acknowledgments and