Study Of The Symmetry In The Coding Sequences Of Beta-trefoil Family And TIM-barrel Family

It is well known that DNA is the carrier of genetic information. The template of protein-coding is mRNA, which carries all the genetic information of protein. Tertiary structures of many proteins are symmetrical, namely, there are similar motifs in protein. From gene evolutionary perspective, this symmetry is due to the results of gene duplication and fusion. Many studies show codon usage in protein-coding sequence is relevant to tertiary structure of the protein. Our task is that symmetrical information of protein tertiary structure is extracted from the protein-coding sequence. We hope further to understand origin of symmetry of protein tertiary structure and to serve for protein structure prediction.In this paper, we focus on the analysis of the protein-coding sequence with similar methods.we study the relationship between the protein-coding sequence, the codon sequence and protein tertiary structure on the aspect of symmetry. Proteins of beta-trefoil family and TIM-barrel family were investigated. Firstly, for beta-trefoil family, tertiary structures of this family protein are triple symmetry and through analysis of their coding sequences, the triple symmetry discovered in the coding sequence was almost as identical as the symmetry of tertiary structure of protein. Secondly, the TIM-barrel family proteins were studied and their tertiary structures mainly present twofold, four-fold and eight-fold symmetry. Analyzing of protein-coding sequences of this family, twofold symmetry was found in all protein-coding sequences and four-fold symmetry was discovered in some. In other protein-coding sequences, due to third similar fragment disappeared in the process of gene evolution, triple symmetry was shown instead of four-fold symmetry. Symmetry discovered in the protein-coding sequences of two families is almost identical to that of protein tertiary structures of two families. All these results support the symmetry of the protein tertiary structure is from hypothesis of ancestral gene duplication. However, no symmetry was found in the codon sequences of proteins of the beta-trefoil family and TIM-barrel family.