The discovery will provide scientists with a better understanding of how to limit uncontrolled cell growth, such as cancer, that might be regulated by controlling the output of ribosomes.
Ribosomes are responsible for the production of the wide variety of proteins that include enzymes; structural molecules, such as hair, skin and bones; hormones like insulin; and components of our immune system such as antibodies.
Regarded as life's most important molecular machine, ribosomes have been intensively studied by scientists. But until now researchers had not uncovered all of the details of how the proteins that are used to construct ribosomes are themselves produced.
In multicellular animals such as humans, ribosomes are made up of about 80 different proteins (humans have 79 while some other animals have a slightly different number) as well as four different kinds of RNA molecules.
Previously, scientists have discovered that the synthesis of the ribosomal RNAs is carried out by specialised systems using two key enzymes: RNA polymerase I and RNA polymerase III.
But until now, scientists were unsure if a complementary system was also responsible for the production of the 80 proteins that make up the ribosome.
This is what the University of California, San Diego researchers headed by Jim Kadonaga, a professor of biology, set out to examine.
They found the missing link - the specialised system that allows ribosomal proteins themselves to be synthesised by the cell.
"We found that ribosomal proteins are synthesised via a novel regulatory system with the enzyme RNA polymerase II and a factor termed TRF2," Kadonaga said.
"For the production of most proteins, RNA polymerase II functions with a factor termed TBP, but for the synthesis of ribosomal proteins, it uses TRF2," Kadonaga added.
"The discovery of this specialised TRF2-based system for ribosome biogenesis provides a new avenue for the study of ribosomes and its control of cell growth, and should lead to a better understanding and potential treatment of diseases such as cancer," Kadonaga said.
The study is published in the journal Genes & Development.