The recent discovery of different types of RNA may soon give us new treatments for viral infections like Hepatitis C and Ebola virus. It also strengthens the case for RNA as a potential major player in astrobiology.
RNA is already a strong candidate for carrying the specific information needed to do the catalytic and genetic functions required by new life. Also, two of its nucleotides—adenine and guanine—form best in ice, which could have helped life get started on Earth and our solar system’s icy moons. I outlined some details in an earlier blog.
As life evolved here on Earth, the 3-D dimensionality of proteins gave them the advantage in taking over structural and catalytic functions, so the nucleic acids have concentrated on reproductive chemistry as life evolved here. DNA—differing from RNA only in its sugar component and one nucleotide (thymine instead of uracil)—was not so easily degraded by enzymes, so RNA was overlooked in the development of drugs to treat diseases.
In the late 20th century, new types of micro RNA were identified that disrupted messenger RNA’s translation process in making proteins. By silencing or crunching some genes, they were determining which proteins would be manufactured in certain cellular environments. This kind of gene regulation is a far cry from RNA’s mechanical functions of translation and transcription, that aid DNA in the manufacture of proteins.
Two new types of RNA now identified are siRNA (small interfering RNA) and microRNA (which replaces messenger RNA to change protein production). IncRNA, an unusually long version of RNA found in the nucleus, is still a mystery. It may have played a role transcribing old or viral inactive DNA Or it may now be playing a role in regulating gene expression by pushing DNA folds around or attaching itself to the DNA in order to change its shape, thus suppressing or triggering its activity.
Most medicines manipulate proteins, but these various RNAs provide a means to attack disease problems at an earlier stage, thus giving us new hope for controlling infections due to viruses and antibiotic-resistant bacteria. The miniRNAs, with patterns taken from specific DNA areas (genes), guide cutting proteins to that specific target on the DNA, thus modifying or disabling it. (Viruses, you’ll remember, are genes wrapped in clever protein that use the host’s DNA to reproduce themselves and make us sick.) These RNA meds attack blood, liver and immune disorders.
The CRISPR system does a direct attack on DNA. In the 1960’s it was found that odd bacterial DNA acting with varied “CAS” proteins defend bacteria from attack by viruses. In 2012 scientists adapted this system so it would guide strands of RNA to cut precise locations in targeted DNA, like that in nasty attack viruses. Potentially, this system could also be used in precise gene therapy, replacing defective with healthy DNA.
What else might these mini RNA’s be capable of? The story is just beginning. As we study astrobiology and the origins of life, we now have the whole new chemical world of miniRNA to consider. With its simpler 2-D, single-stranded structure, RNA may be flexible enough to have jump-started life on our solar system’s most likely places, including Earth, and maybe Enceladus or Europa or Titan.
See Scientific American April 2014, pp.54-59 and “Some consequences of the RNA world hypothesis,” by L. E. Orgel in 2003 Orig.Life Evol. Biosphere 33:211-218.