Biologists have discovered the “missing link” in the chemical system that allows animal cells to produce ribosomes, our protein factories. The findings could help us understand how to limit uncontrolled cell growth.
Thousands of ribosomes are contained in our cells, and they’re responsible for making all the proteins needed to build tissues and sustain life. That includes the production of enzymes, antibodies, hormones like insulin, and structural molecules, like hair, skin, and bones. Ribosomes are considered one of life’s most important molecular machines, yet we still don’t know all the details about how they’re made.
In humans, ribosomes are made of 79 different proteins (other multicellular animals have a slightly different number) in addition to four different kinds of RNA molecules. Decades ago, scientists discovered that synthesis of ribosomal RNA is carried out by specialized systems using two key enzymes: RNA polymerase I and RNA polymerase III. But until now, scientists didn’t know if a complementary system was producing the 80 or so proteins used to construct ribosomes.
Now, a team led by Jim Kadonaga from the University of California, San Diego, discovered a specialized system that allows ribosomal proteins themselves to be synthesized by the cell.
The novel regulatory system uses the enzyme RNA polymerase II and a factor called TRF2. For the production of most proteins in the body, RNA polymerase II functions with TBP (for TATA box-binding protein) -- but it uses TRF2 specifically for the synthesis of ribosomal proteins.
Here’s a schematic of the complementary systems:
“The discovery of this specialized TRF2-based system for ribosome biogenesis,” Kadonaga says in a press release, “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.”
The work was published in Genes & Development this week.