Genome complexity: transposons can make ribozymes (Introduction)

by David Turell , Tuesday, December 24, 2019, 18:32 (1577 days ago) @ David Turell

In what was so-called junk DNA, it is found transposons, jumping genes, can make functional ribozymes:

https://phys.org/news/2019-12-reveals-role-genes-stress.html

"Only percent of human DNA codes for proteins, and approximately half of the rest of the genome is made up of what used to be called "junk" sequences that can copy themselves into RNA or DNA and jump from one location to another. Previous research led by investigators at Massachusetts General Hospital (MGH) had revealed a critical role for one of these jumping genes during times of stress.

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"The sequences that jump from place to place in the genome are more formally known as transposable elements, and their role in health and disease is not fully understood. But it has long been suspected that they are more than just parasitic elements without good function. In their original study, Jeannie Lee, MD, Ph.D., an investigator in the Department of Molecular Biology at MGH, and her colleagues found that one of these transposable elements—a very abundant, short interspersed nuclear element (SINE) called B2 in mice (ALU in humans)—makes an RNA that is cut when together with a protein called EZH2. However, at the time, they did not know how the RNA is cut. Researchers now make the striking discovery that B2 and ALU cut themselves.

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"Today, 15 classes of ribozymes have been described, but they are mostly observed in bacteria and viruses. Very few are known in mammals such as humans, and their functions are mostly unclear.

"Because B2 and ALU are so abundant in our cells, the Lee group's discovery puts a new twist to the ribozyme story. "B2 and ALU are present in hundreds of thousands of copies in our DNA and they become massively expressed during stress. This is a mind-boggling amount of ribozyme activity," said Lee. The team found that B2 and ALU are normally silent, but when subjected to heat or other forms of stress, they become activated. Also, their RNA-cutting activity is enhanced by an interaction with the EZH2 protein.

"Lee noted that cells are continually challenged by stress, and a swift response can mean the difference between life and death. "Hinging the induction of stress-related genes to self-cutting RNAs seems highly adaptive," she said. "No new synthesis of gene products would be required and the critical event would instead be the recruitment of a protein factor, EZH2, that already exists inside cells and stands ready to be mobilized.'"

Comment: The genome is like an onion, layers and layers of control discovered and stil to be discovered. This complexity is not the result of chance evolution.