Young unmarried girls used to be accompanied by chaperones at social events. Their task was to prevent their charge from having undesirable romantic rendezvous with young boys. The term "molecular chaperones" is used in cellular biology to refer to a group of proteins which prevent undesirable contact between other proteins. Such contact can be particularly dangerous during protein production, a process carried out by the ribosome in the cell. The ribosome functions like a knitting spool: 20 different amino acids are threaded together like loops of thread in various sequences and amounts. The emerging amino acid chain disappears into a tunnel and does not come back out until it has reached a certain length.
A research group led by Freiburg biochemist Prof. Dr. Sabine Rospert studies how the chaperones at the end of the ribosomal tunnel influence the fate of newly synthesized proteins and how their functioning is coordinated in time and space. In 2005, the group discovered the chaperone ZRF1 at the end of the human ribosomal tunnel. ZRF1 exhibits structural characteristics which are otherwise typical only of proteins which influence the chromatin structure. Chromatin is a combination of DNA, histone, and other proteins in the nucleus of the cell. The DNA contains the information necessary for letting a ribosome know which amino acid chain it should produce. Gene segments of the DNA are translated into transcripts for this purpose, which then leave the nucleus in order to program the ribosomes for the synthesis of certain proteins.
Why does a chaperone sitting at the end of the ribosomal tunnel need to possess characteristics that can influence the chromatin structure in the nucleus? Thanks to the cooperation between Sabine Rospert's team in Freiburg and a group of researchers working under the biologist Prof. Dr. Luciano Di Croce at the Centre for Genomic Regulation in Barcelona, Spain, scientists are now a step closer to answering this question. Di Croche investigates protein complexes which influence the chromatin structure and thus also the production of transcripts. Reversible modifications to histone proteins in the chromatin play a decisive role in these processes. The experiments conducted by the scientists have revealed that ZRF1 influences the modification of a histone protein, thus allowing the production of a specific group of transcripts for a limited period of time.
These results, published in the current issue of the journal Nature, constitute an important step in the quest to understand the connection between the function of ZRF1 in the ribosome and in the chromatin. The discovery that this molecular chaperone has a dual function, both in the process of transcription and in the translation of the transcripts into proteins at a different place and time, is important initial evidence for the assumption that there is a link between the regulation of the two processes.
- Holger Richly, Luciana Rocha-Viegas, Joana Domingues Ribeiro, Santiago Demajo, Gunes Gundem, Nuria Lopez-Bigas, Tekeya Nakagawa, Sabine Rospert, Takashi Ito, Luciano Di Croce. Transcriptional activation of polycomb-repressed genes by ZRF1. Nature, 2010; 468 (7327): 1124 DOI: 10.1038/nature09574
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