I’ve posted a couple of times on the origin of life and its relation to evolution. Since those posts my curiosity has been aroused even more and have kept an eye out for more advances in theories pertaining to the origin of life. In this post I made a reference to the theory of an RNA world and it is that theory on the origin of life that I want to discuss today. The details of how DNA and RNA interact to define and form the proteins of new cells is beyond the scope of this article, but the wikipedia articles linked above are fine resources.
Briefly, the theory of an RNA world is that before DNA existed all gene expression in cells occurred through the use of RNA. Previously one of the big questions about this theory, which is a result of DNA’s prevalence in all life as we know it, was “If proteins are needed to carry out life’s functions and DNA is needed to make proteins”, how would RNA be sufficient for gene expression? (1)
A new study in the peer-reviewed journal Science has recently brought light to this question. While studying bacterial cells that can express a wide range of behavior “including cell differentiation, conversion between motile and biofilm lifestyles, and virulence gene expression” without early involvement of DNA, scientists at Yale University have discovered how RNA in the bacteria can cause genes to be expressed without the use of proteins.(2)
Breaker et al have shown that messenger RNA which control these behaviors can respond to the presence of an RNA dinucleotide (its made up of only 2 nucleotides) called cyclic di-guanosine monophosphate or cyclic di-GMP for short. This ability was long thought to be exclusive to proteins. One important example of the use of cyclic di-GMP in bacteria is in the cholera causing bacteria, vibrio cholerae, in which the presence of cyclic di-GMP suppresses the bacterias ability to create the necessary sugar-binding proteins responsible for the bacterias ability to “colonize mammalian intestines.”(2)
This is a very strong advancement for the RNA world theory because it helps to alleviate, if not remove, the strong need for DNA in the earliest stages of evolving life because genes can be expressed without the use of proteins.
We get ever closer to explaining the origins of life. Damn, this is exciting stuff!
1. Researchers Discover Remnant of an Ancient ‘RNA World’. ( July 17, 2008 ). http://www.physorg.com/news135522723.html
Science 321 (5887), 411. [DOI: 10.1126/science.1159519]