New findings have shown that amino acids, the building blocks of proteins, can be assembled without instructions from the DNA or RNA.
A protein, Rqc2, has been detected playing a role similar to that of the messenger RNA, calling for a rewriting of biology textbooks.
Using a cryo-electron microscopy to flash freeze and then visualise the machinery in action, researchers from the University of Utah Health Sciences saw a protein directing the quality control process in a cell.
Ribosomes work to link amino acids on a protein assembly line, going by an order specified by the genetic code. When things go wrong, the ribosome stalls the assembly process until the quality control crew reaches the site.
Eventually the ribosome is disassembled, the blueprint discarded and the partly made protein is recycled.
But the team saw that before the protein is recycled, a protein conserved from yeast to man called Rqc2 prompts the ribosomes to add just two amino acids (of 20 total) – alanine and threonine - over and over, and in any order.
The researchers suspect that the seemingly random sequence is part of a design and could be a code to signal that the protein must be destroyed, or a test to check the ribosome.
Either or both of these processes could be faulty in neurodegenerative diseases such as Alzheimer's, Amyotrophic lateral sclerosis (ALS), or Huntington's.
New RNA sequencing techniques showed that the Rqc2/ribosome complex also bound tRNAs, structures that bring amino acids to the protein assembly line. This showed the complex had the ability to add amino acids to proteins.
All the stalled proteins had extensive chains of alanines and threonines added to them.