It has long been textbook knowledge that the DNA serves as the blueprint that gives out the instructions for the production of proteins inside the body, but findings of a new research defies this gospel in molecular biology by providing evidence that some proteins have the ability to make other proteins.
Results of a new study published in the journal Science on Jan. 2 shows for the first time that amino acids, known as the building blocks of protein, can be assembled without DNA and messenger RNA (mRNA), which is known to carry the instructions for the assembly of the amino acids.
Peter Shen from the University of Utah and colleagues observed a case when another protein exhibited a role similar to that of the mRNA. For people to understand the process inside the cell, the researchers likened it to that of a factory where the ribosomes act as machines on the protein assembly line.
The ribosomes link together the amino acids according to the order given by the genetic code and stall when anything goes wrong. When this happens, quality control has to disassemble the ribosomes, discard the blueprint and recycle the partly made protein.
The researchers' study, however, showed that a protein known as Rqc2, a member of the quality control team, has a surprising role. Before the partly made protein is recycled, the Rqc2 instructs the ribosomes to add only two amino acids, threonine and alanine, out of a total of 20, over and over and in any order so the assembly line continues its operation regardless that it has lost the instructions.
"In this case, we have a protein playing a role similar to that filled by mRNA," said study researcher Adam Frost from the University of Utah.
A half-made protein with a random sequence of threonines and alanines may not properly work, but the researchers suspect that what appears to be a random sequence could be a code that prompts the truncated protein to be destroyed. It is also possible that it may have been part of a test that would determine if the ribosome works properly.
"Our work uncovers an unexpected mechanism of protein synthesis, in which a protein -- not an mRNA -- determines tRNA recruitment and the tagging of nascent chains with carboxy-terminal Ala and Thr extensions," the researchers wrote.
Individuals with neurodegenerative diseases, such as Lou Gehrig's, Huntington's and Alzheimer's diseases, have proteins with defective quality control processes. Knowing the exact conditions that trigger Rqc2 could pave the way for the development of new treatments for these conditions.
