Molecular Basis of RNA-Dependent RNA Pol II Activity

Transcription is the process wherein DNA is turned into messenger molecules which serve as template for protein synthesis. During transcription, DNA sequence is enzymatically copied by RNA polymerase (Pol) II to produce a complementary nucleotide RNA strand. However, there are evidences that Pol II can also synthesize RNA nucleotides using RNA templates. A group of German scientists have elucidated the molecular basis of RNA-dependent RNA Pol II (RdRP) activity.

Crystallographic analysis of Pol II showed that the RNA template and the newly synthesized RNA strand occupy the same position in the enzyme as the DNA template and its RNA counterpart during normal transcription. However, RdRP is slower and less processive than DNA-dependent activity. The researchers noted that the RdRP activity of Pol II provides a missing link in molecular evolution, as the unexpected use of RNA templates by Pol II can explain the switch from RNA genomes to DNA genomes billions of years ago. RdRP is still being used by numerous plant viroids to replicate their genomes.

The full paper published by Nature is available at http://www.nature.com/nature/journal/v450/n7168/pdf/nature06290.pdf Non Subscribers can read the abstract at http://www.nature.com/nature/journal/v450/n7168/abs/nature06290.html