Book of Abstracts: Albany 2005
Introns are Inserted into Nucleosome DNA
Introns comprise large portion of eukaryotic genome (∼30% of human genome). Their origin is unknown. There are two main hypotheses about the time of intron incorporation: ?introns early? -- stating that they exist in early cells and were subsequently lost in prokaryotes and ?introns late? -- stating that they invaded eukaryotes after the separation from prokaryotes. There are conflicting opinions about the importance of introns in cell functioning. Some relate to them as junk DNA. Others thought them to be an essential part of chromatin structure. Following the ?introns late? line of thought and previously discovered connection between nucleosome positioning and gene splicing, this work investigates the possibility of intron insertion into DNA sequences bound in nucleosomes and subsequent changes in nucleosome positioning DNA sequence pattern.
Using large data base of protein-coding intron-containing DNA sequences, we show, by examination of the phase of nucleosome positioning DNA sequence pattern in the vicinity of splice junction, that introns appear to be incorporated in those places where nucleosomes have being positioned before the intron insertion. This phenomenon supports ?introns late? hypothesis. The result is highly statistically significant despite the limitations of currently available nucleosome positioning methods. We analyze also the difference between intron sequences in the vicinity of exon-intron and intron-exon splice junctions from the point of view of nucleosome positioning signal. Finally, we discuss the possible reasons of the above intron insertion and the role that introns play in cell functioning.
Genome Diversity Center