In a cell DNA contains the genetic code that is used to build proteins.
The cell creates mRNA, a DNA copy, to build proteins. A molecule known as a ribosome then reads the DNA, translating it to protein. This step was a mystery to scientists: they didn’t know exactly how the ribosome attached and read mRNA.
A team of scientists from around the world, including researchers at University of Michigan, has used advanced microscopy techniques to visualize how ribosomes attach to mRNA as it is being transcribed using an enzyme known as RNAP. The results of their study, which examined the process within bacteria, were published in Science. Albert Weixlbaumer is a co-author of the
“Understanding how the ribosome captures or ‘recruits’ the mRNA is a prerequisite for everything that comes after, such as understanding how it can even begin to interpret the information encoded in the mRNA,” study. He’s a French researcher at Institut de genetique et de biologie moleculaire et cellulaire. Researchers discovered “It’s like a book. Your task is to read and interpret a book, but you don’t know where to get the book from. How is the book delivered to the reader?”
This is necessary for the start of the protein synthesis. It is like a supervisor at a building site ensuring that workers install a complicated section, and confirming twice in a row to ensure maximum functionality. According to researchers, understanding these basic processes can lead to new antibiotics targeting these pathways.
Antibiotics traditionally target the ribosome, or RNAP. However, bacteria have evolved and mutated to develop resistance to these antibiotics. The team is hoping to defeat bacteria with the new information they have gained. Adrien Chauvier is a senior scientist at U-M and one of the four study co-leaders. “We could target this interface, specifically between the RNAP, ribosome, and mRNA, with a compound that interferes with the recruitment or the stability of the complex.”
To show the mechanism of how components work in concert to deliver freshly transcribed transcripts to the ribosome, the team created a framework that explains the interactions between the different parts. Weixlbaumer explained. “Using purified components, we reassembled the complex — 10-billionth of a meter in diameter. We saw them in action using cryo-electron microscopy (cryo-EM) and interpreted what they were doing. We then needed to see if the behavior of our purified components could be recapitulated in different experimental systems.”
“Using purified components, we reassembled the complex — 10-billionth of a meter in diameter. We saw them in action using cryo-electron microscopy (cryo-EM) and interpreted what they were doing. We then needed to see if the behavior of our purified components could be recapitulated in different experimental systems.”
“Using purified components, we reassembled the complex — 10-billionth of a meter in diameter. We saw them in action using cryo-electron microscopy (cryo-EM) and interpreted what they were doing. We then needed to see if the behavior of our purified components could be recapitulated in different experimental systems.”
“interpreter,” “interpreter,”DNA is located in the nucleus of more complex cells. RNAP breaks down the genetic instructions to smaller pieces. The enzyme is a dynamo that transcribes or writes DNA, a specific copy of which is then moved to the ribosome, located in “roomier” the much larger cytoplasm. From there, it’s translated into the building blocks of living proteins. The RNAP, the ribosome, and transcription all occur simultaneously in prokaryotes. This is because prokaryotes lack a nucleus or an internal membrane.
Bacteria, the most well-studied of the prokaryotes and with their simpler genetic structure provided an ideal environment for the research team to study the mechanisms involved in ribosome and RNAP coupling. Researchers used different technologies to study the process. The Berlin lab employed Andrea Graziadei’s crosslinking mass spectrometry in cells, while Weixlbaumer’s team utilized cryo-EM. Chauvier, a biophysicist, and Nils Walter of U-M’s chemistry, biology, used their single-molecule fluorescence microscopy to examine the kinetics.
“In order to track the speed of this machinery at work, we tagged each of the two components with a different color,” Chauvier said. The researchers observed that RNAP bound the mRNA to the 30S small ribosomal unit more efficiently if ribosomal proteins bS1 were present. This helped the mRNA unravel in preparation for the translation within the ribosome. Webster’s and Weixlbaumer’s cryo-EM structure revealed an alternate pathway for mRNA transport to the ribosome. This involves the tethering RNA polymerase with the coupling transcription factors NusG or RfaH.
These proteins thread the mRNA through the mRNA entrance channel of the ribosome on the opposite side of bS1. The team is looking forward to further collaboration in order to determine how to rearrange the complex to make it fully functional. Walter. Huma Rahil was a PhD student at the Weixlbaumer Lab and Michael Webster is now a researcher with The John Innes Centre, in United Kingdom. They also co-authored the paper.
