While most ribosome assembly takes place in the nucleolus, a protein-nucleic acid structure inside the nucleus, the final maturation process occurs in the cytoplasm, the "general" cellular compartment where protein translation occurs. In the cytoplasm, these pre-mature ribosomal subunits encounter large pools of mature subunits, messenger RNA, and various translation factors.
This cellular stew presents a unique challenge, especially keeping the translation process from acting on the subunits prematurely, which would result in their rapid degradation or in the production of incorrectly assembled proteins, both processes with potentially lethal outcomes for the cell.
The new study shows that that the bound assembly factors cooperate with one another in a highly redundant and multi-pronged approach to prevent such occurrences, chaperoning the pre-40S subunits to keep them from falling victim to the translational apparatus.
"We had thought the role of assembly factors was to help mature this intermediate form of the ribosome," said Karbstein. "But our new research has shown that these assembly factors also prevent a number of unwanted things from happening. If one of these intermediate forms were to bind prematurely to a messenger RNA, there could be no protein produced, or worse, a wrong protein might be produced and that could lead to early cell death."
It's important to note that this is a single snapshot of the late-stage assembly process, Karbstein added. "We know better how the process works but this is by no means a final statement," she said.
|Contact: Mika Ono|
Scripps Research Institute