Research On Evolutionary Relationship And Code Words Of Microrna

MicroRNA is a class of endogenous～22 nt small non-coding RNA, whichwidely exists in eukaryotic genomes. Mature microRNA is processed frompre-miRNA of hairpin structure. MicroRNA genes have three basic characters:conservation, clustering occurrence and space-time specific expression. MaturemicroRNA regulates gene expression by targeting mRNA for cleavage ortranslational repression, playing important regulatory role in the development ofanimals and plants, the proliferation and death of cells, the differentiation of cells andthe cancer therapy. In the latest years, the prediction of microRNA gene and its targetgene has become a research hotspot. In this paper we developed a new systematicmethod to explore the sequence evolution of microRNA and the code words inherentin the genes. The paper is devided into three parts:In the first part of the paper an overview of microRNA is given from thebiological property, the synthetical process, the active mechanism and the function ofthese genes. The present status of the microRNA study is also outlined. In the second part we have deduced the microRNA cladograms of 18 species byconstructing fuzzy equivalent relation based on Pearson correlation coefficient,Spearman correlation coefficient and a new definition of sequence distance betweenspecies. These three cladograms describe the evolutionary relation of microRNAgenes. We find the cladograms of 8-mer based on Spearman correlation and distancedefinition are consistent with the actual evolution relation among species.In the third part we have investigated 8-mer coding modes of microRNA indetail at different confidence levels. It includes the study of coding modes laterally ingiven species and the study of family-specific coding modes longitudinally. We findthat two kinds of 8-mer code words, the species code words and the family codewords together can give a full description of the property of 22nt microRNA code.Furthermore, we find that the first half of microRNA sequence is more conservativefrom D₁,D₂ distribution map, which can be explained by the position of microRNAseed sequence.