07.04.2017 change 07.04.2017

The role of spools on which the DNA strands are coiled better understood

If DNA was not properly and accurately coiled in our cells, it would probably make quite a mess there! Researchers from Adam Mickiewicz University have investigated the role of the spools on which the genes are coiled. It turns out that these structures play an important, previously unknown role in both activation and deactivation of genes.

"DNA molecules are very long! If we were to unwind just the first human chromosome, we would receive an 8.5 cm long thread" - said Dr. Piotr Ziółkowski from Adam Mickiewicz University. In addition, we have not one, but as many as 23 pairs of chromosomes, corresponding to a total length of more than 2.2 meters of DNA in virtually every cell (adult person has about 37 trillion cells). And yet the cells are tiny! Some of them have a volume of just 7 microns, which is almost 200 times smaller than a pin head. How come DNA does not tangle and fit properly into the tiny nucleus of the cell? And in addition, it is possible to reach any information and produce the right proteins.

This all happens with the help of nucleosomes - the spools on which the DNA is coiled. Nucleosomes are made up of proteins - histones. They are so crucial for the proper functioning of the body that they have not changed much in the course of evolution. These proteins look almost the same in plants as in humans. And for scientists this is a signal that they are very important for the functioning of the cell.

For a long time scientists thought that these structures were just scaffoldings for DNA. But for nearly 30 years it has been known that DNA related to proteins of these spools also regulate gene expression.

Researchers from Adam Mickiewicz University focused on one of such "spool" proteins - histone H2A.Z. Previously, scientists did not agree on the role of nucleosomes containing H2A.Z. Some believed that these proteins help activate genes, while other studies indicated that, on the contrary, they have a role in gene deactivation. "We were the first to demonstrate that this variant of histone can have both of these opposing roles" - commented Dr. Ziółkowski in an interview with PAP. His research was published in March in The Plant Cell.

The researcher from Adam Mickiewicz University explained that H2A.Z histones are found not only in the spool at the beginning of each gene, but there are a lot of these proteins along the genes that are responsible for environmental stress.

The researchers investigated how the protein would function when, for example, the plant was placed in an overly salted environment - under osmotic stress conditions. It turned out that plants with a limited amount of histone H2A.Z germinated much later than ordinary plants. "They could not adequately coordinate the activation and deactivation of genes in response to drought" - said Dr. Ziółkowski.

Research of Polish scientists shows that the histone has different functions at the beginning of the gene - it enables unwrapping DNA strand from the spool and initiating the process leading to gene expression. But in the rest of the gene the histone has a completely different function. It actually prevents accidental unwinding of the thread and consequently unwanted protein production. The authors have discovered that under stress conditions, H2A.Z is thrown out from the spools along the genes that should be activated, thereby enabling their efficient expression. "We still do not understand the reasons for the different functions of H2A in nucleosomes located at the beginning and along the gene" - concluded Dr. Ziółkowski.

PAP - Science and Scholarship in Poland, Ludwika Tomala

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