Defying textbook science, study finds new role for proteins

[n2doc]

Open any introductory biology textbook and one of the first things you'll learn is that our DNA spells out the instructions for making proteins, tiny machines that do much of the work in our body's cells. Results from a study published on Jan. 2 in Science defy textbook science, showing for the first time that the building blocks of a protein, called amino acids, can be assembled without blueprints - DNA and an intermediate template called messenger RNA (mRNA). A team of researchers has observed a case in which another protein specifies which amino acids are added.

"This surprising discovery reflects how incomplete our understanding of biology is," says first author Peter Shen, Ph.D., a postdoctoral fellow in biochemistry at the University of Utah. "Nature is capable of more than we realize."

To put the new finding into perspective, it might help to think of the cell as a well-run factory. Ribosomes are machines on a protein assembly line, linking together amino acids in an order specified by the genetic code. When something goes wrong, the ribosome can stall, and a quality control crew is summoned to the site. To clean up the mess, the ribosome is disassembled, the blueprint is discarded, and the partly made protein is recycled.

Yet this study reveals a surprising role for one member of the quality control team, a protein conserved from yeast to man named Rqc2. Before the incomplete protein is recycled, Rqc2 prompts the ribosomes to add just two amino acids (of a total of 20) - alanine and threonine - over and over, and in any order. Think of an auto assembly line that keeps going despite having lost its instructions. It picks up what it can and slaps it on: horn-wheel-wheel-horn-wheel-wheel-wheel-wheel-horn.

more

http://phys.org/news/2015-01-defying-textbook-science-role-proteins.html

[phantom power]

1. extremely cool, but not really that shocking

There's nothing magic about ribosome mechanism that some other molecule with the right shape couldn't accomplish. For example, a protein.

[Lionel Mandrake]

2. I'm underwhelmed.

Adding a random sequence of adenines and threonines is hardly a substitute for what mRNA does, which is to specify a precise sequence of amino acids of 20 varieties.

What's more interesting (and well known) is that some RNA transcripts of DNA are not translated into proteins, but instead act directly as enzymes (a role usually performed by proteins). These so-called ribozymes include the main components of ribosomes. This fact is evidence that RNA came before proteins, i.e., there was once an RNA World.

Read more:
http://en.wikipedia.org/wiki/RNA_world_hypothesis