In all living creatures, except for bacteria, the genetic material, called DNA, contains regions which do not code for any message (protein). After transcription of DNA into RNA called pre-messenger RNA (pre-mRNA), this RNA still contains these non-coding regions (introns). The introns have to be removed from the pre-mRNA and the coding regions (exons) have to be joined together in order to yield mature messenger RNA, which can then be translated into proteins. This process is called splicing and is performed by a huge complex called the spliceosome.
The spliceosome is a dynamic complex and is composed of five different complexes called small nuclear ribonucleoproteins (snRNPs or “snurps”). Splicing involves a two-step biochemical process to cleave the intron and splice the exons. One highly conserved RNA building block, called branchpoint adenosine, which is present in the intron acts as a scissor to cut the RNA between the exon and the start of the intron. Next the freed exon is the scissor and cuts between the end of the intron and the following exon thus joining the two exons and liberating the intron. In each step of the splicing process different snRNPs and proteins are involved. Although splicing is a very important process for the proper flow of genetic information from DNA into proteins not much is understood about how it really works.
To obtain better insight into the precise mechanism of splicing it is important to obtain structural snapshots of proteins that are important during the splicing reactions. The structure of these proteins alone might not reveal the secrets of splicing but they are pieces of a puzzle and with enough pieces the puzzle can be solved. In my research project I solved the structure of a protein (called Rds3), which sits in close proximity to the branchpoint adenosine. The structure of Rds3 is very interesting because it has never been seen before in any other protein. The structure resembles a triangle with a metal ball (zinc ion) in each corner for stability and most unusual the backbone of the protein has formed a knot like a tied shoelace (see figure 1). Not many proteins are known to tie themselves into a knot. The structure looks a little bit like the triquetra symbol (http://en.wikipedia.org/wiki/Triquetra).
