The tRNAs were divided into 62 groups based on the codons they carried and networks were constructed. Phylogenetic trees were constructed in parallel and antiparallel directions based on the parameters of these networ...The tRNAs were divided into 62 groups based on the codons they carried and networks were constructed. Phylogenetic trees were constructed in parallel and antiparallel directions based on the parameters of these networks. Point mutations were found in the codon sites in the same clusters in the entire parallel and antiparallel phylogenetic trees, whereas there was no evidence of a complementary duplication mechanism in the corresponding antiparallel phylogenetic trees. The codons of isoaccepting tRNAs were found in neighboring clusters or distributed within a very small distance so the codons with only one base difference remained very close, which was perfectly consistent with the hypothesis that a new tRNA gene could be recruited from an isoaccepting group via another point mutation.展开更多
Many theories thought that present-day tRNA sequences evolved from some short RNA hairpins which contain a simple stem-loop structure. To find out these significant fragment sequences, the repeated sequences of differ...Many theories thought that present-day tRNA sequences evolved from some short RNA hairpins which contain a simple stem-loop structure. To find out these significant fragment sequences, the repeated sequences of different length within 3420 tRNA sequences are counted and analyzed. The results show that: 1) the probability of occurrence P(i) with the given repeated sequences i follows a power-law distribution when the length K of repeated sequences is longer than four bases, and in this case, the total number N(n) of occurrence with the repeated times n follows a power-law distribution too;2) the sequence of the length K which repeats the largest times is just only sequence of the length K-b wobbling b bases on its left or right side (b varies between 1 and K-1);3) the same repeated sequences are found nearly at the identical site in different tRNA sequences as the length K of repeated sequences is longer than five bases. Then a hypothesis of the origin and evolution mechanisms of tRNA sequences is proposed and discussed.展开更多
文摘The tRNAs were divided into 62 groups based on the codons they carried and networks were constructed. Phylogenetic trees were constructed in parallel and antiparallel directions based on the parameters of these networks. Point mutations were found in the codon sites in the same clusters in the entire parallel and antiparallel phylogenetic trees, whereas there was no evidence of a complementary duplication mechanism in the corresponding antiparallel phylogenetic trees. The codons of isoaccepting tRNAs were found in neighboring clusters or distributed within a very small distance so the codons with only one base difference remained very close, which was perfectly consistent with the hypothesis that a new tRNA gene could be recruited from an isoaccepting group via another point mutation.
文摘Many theories thought that present-day tRNA sequences evolved from some short RNA hairpins which contain a simple stem-loop structure. To find out these significant fragment sequences, the repeated sequences of different length within 3420 tRNA sequences are counted and analyzed. The results show that: 1) the probability of occurrence P(i) with the given repeated sequences i follows a power-law distribution when the length K of repeated sequences is longer than four bases, and in this case, the total number N(n) of occurrence with the repeated times n follows a power-law distribution too;2) the sequence of the length K which repeats the largest times is just only sequence of the length K-b wobbling b bases on its left or right side (b varies between 1 and K-1);3) the same repeated sequences are found nearly at the identical site in different tRNA sequences as the length K of repeated sequences is longer than five bases. Then a hypothesis of the origin and evolution mechanisms of tRNA sequences is proposed and discussed.
