11 March 2011

A film about the work of the spliceosome: down to the molecule

A technique has been developed to monitor molecular processes in real time
Kirill Stasevich, Compulenta

The five-year work of several American laboratories has led to an impressive result: from now on, biologists can follow an individual protein molecule through a microscope. The molecular process for which the equipment and methodology were developed is called splicing, or, in other words, maturation of matrix RNA.

In a nutshell – what exactly is going on. The cell synthesizes a protein not on a gene – a section of DNA, but on an intermediary molecule - matrix RNA. First, an RNA copy, a matrix RNA, is removed from the DNA, on which the polypeptide - protein –chain is then assembled. But between the synthesis of the matrix RNA and the synthesis of the protein molecule, the RNA molecule undergoes splicing. The fact is that the information in the genome is packed extremely tightly, and DNA in this sense can be likened to archive files; the same part of the molecule can encode several different proteins, fragments of the genetic code of which are written randomly with each other.

These fragments of information about different proteins may coincide, may partially overlap, but one thing is important: during the synthesis of RNA, they are all rewritten to the RNA molecule in the form in which they are in DNA. When it comes to protein synthesis, the matrix RNA molecule should contain a sequence of only one protein, without gaps, seams and pieces of someone else's code. Here, splicing just performs the function of cutting out "unnecessary" pieces from the matrix RNA.

For clarity, we can imagine that we have a chemistry textbook and a cookbook, intertwined with each other so that the pages of the two editions are mixed. So, during splicing, unnecessary pages are cut out and the text is restored into a single meaningful whole, and as a result we can read what we need – a textbook or a collection of recipes.

Like everything that happens in a living cell, splicing requires the participation of huge protein complexes. The protein complex that performs this procedure is called a spliceosome.

It should work with extraordinary precision, because the slightest mistake in cutting-stitching will lead to the synthesis of a non-working or incorrectly working protein. The study of the spliceosome is important for applied medical purposes, but it does not make it easier to study it: the full cycle of operation of this complex is still unknown. Now, after the appearance of a tracking system for an individual protein molecule, the task is simplified several times. The method was tested on a yeast splicing system.

In the laboratory of researcher Virginia Cornish at Columbia University, a fluorescent dye was created that labeled individual proteins of the spliceosome. Jeff Jellen's group at Brandeis University designed a laser that excited a dye on a protein molecule, and an optical microscope with which it was possible to observe the glow of a protein molecule with a dye. You can mark different components of a large protein complex with different dyes and monitor their behavior in real time: who, with whom, when and in what order it occurs and on which part of the RNA molecule it occurs.

It cannot be said that the idea of the method itself is so new. But in this case, the task was not to offer a general idea, but to find a specific solution: it was necessary to find a dye that would not damage the protein and not disrupt its function, learn how to "dye" protein molecules, construct a microscope... A report on the work of American scientists was published on March 11 in the journal Science (Ordered and Dynamic Assembly of Single Spliceosomes).

This technology, of course, will go beyond the narrow (albeit important) study of splicing; the developers plan to introduce it into all branches of molecular biology. Even now, Mr. Jellen and his colleagues are trying to "see" transcription proteins – the process by which RNA is synthesized. It is unlikely that biologists will refuse such a gift: they have a chance to replace all the cartoons about DNA, RNA, ribosomes, etc. with a real documentary.

Prepared based on the materials of PhysOrg: Lasers, custom microscope show gene splicing process in real time.

Portal "Eternal youth" http://vechnayamolodost.ru11.03.2011

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