DNA Is a Code Operated by Another Code
The discovery in the 1950s that DNA stored a coded language was amazing, but recently a new level of complexity has come to the awareness of biochemists. Apparently, another code determines which DNA genes will be opened for expression and which should be suppressed.
The Feb. 14 issue of Science News1 describes the history of the discovery of the so-called “histone code.” These are patterns of “tails” attached to the histones around which DNA is tightly wrapped. Within the last eight years, scientists have been discovering that the histones do not merely spool the DNA, they regulate which genes get expressed.
The pattern of acetylation and methylation on the histone tails appears to form a code that is heritable through cell divisions. Compared to the well-known DNA genetic code, “A histone code may be much more complex,” writes John Travis. Shelley Berger (Wistar Institute) exclaimed, “There are all kinds of sites [on histone tails] that can be modified. The possibilities for a code are quite enormous. It’s not going to be a simple code.” After summarizing the literature, Travis concluded, “With such designer histones, it seems that researchers are on their way to having in their hands all the words of the histone code. But, it may still be a stiff challenge to figure out what those words mean.”
For a previous story on the histone code, see 11/04/2002, “Cell Memory Borders on the Miraculous.”
1John Travis, “Code Breakers: Scientists tease out the secrets of proteins that DNA wraps around,” Science News, Vol. 165, No. 7, Feb. 14, 2004, p. 106.
Evolutionary biologists had their hands full explaining the origin of the DNA-protein language, and now this. As usual, there is no description in the article about how this code might have “emerged” through an evolutionary process. There is only the following quip, that not only fails to explain the code’s origin, it adds another problem: apparently the code has not evolved at all: “From species to species, he [C. David Allis, U. of Virginia] notes, these tails are nearly identical, implying that they are important to the cell. ‘Nature has held these things constant for a reason,’ says Allis.” Certainly. Give me a working histone code in the beginning, or give me death.