Comparetive Analysis Of Essential And Nonessential Genes In Escherichia Coli K-12

There are many genes in the genome of a species, only the smallest genome which present know contains 482 genes. Those genes are not only different in their function, but also have different contribution to the living and propagation of the organism. Genes can be classified essential and nonessential based on their indispensability for a living organism. The research of essential genes is important in biology, and can explore the genesis of life and provide designing antibacterial with theoretical groundwork.Three decades ago, Wilson et al. proposed that genes which differ in their indispensability to the organism will have different rates of evolution, and essential genes evolving more slowly than nonessential genes. This has more recently been termed the"knockout-rate"prediction. Then, more and more biologists focused on testing the prediction and exploring the relationship between gene importance and evolution rate. Despite most studies show that the more important gene evolving more slowly, there are some controversial evidences. The importance of genes are often weak correlated with the evolutionary rate, and furthermore that a gene's rate of evolution can't be used to estimate the importance of a gene and fail to predict it can be classified as essential or nonessential. To better understand of the evolution mechanisms of essential genes, we performed an investigation into the properties of essential and nonessential genes, and help to distinguish essential genes from nonessential genes in molecular evolution. As a preferred model organism, Escherichia coli k-12 was comprehensively studied, and provided a platform for genetic, biochemical and molecular evolution research. Through analysis of evolutionary conservation, protein length distribution, amino acid usage and function between essential and nonessential genes in Escherichia coli we obtained those following results:(1) Essential genes are relatively preserved throughout the bacterial kingdom when compares to nonessential genes, which confirmed the"knockout-rate"prediction.(2) Essential genes , compared to nonessential genes, have a higher proportion of small (﹤139 amino acids) and large (﹥534 amino acids) relative to medium-sized proteins in Escherichia coli.(3) The pattern of amino acids usage shoes a similar trend for essential and nonessential genes, although some notable discrepancies are shown. (4) Sixteen amino acids have significant differences in degree of usage between essential and nonessential genes, and five amino acids——Asp(D), Glu(E), Lys(K), Arg(R) and Val(V), are of greater usage in essential genes, all of which are preferred amino acids in both types of genes, expect Lys.(5) Four of amino acids which are found in higher proportions in essential genes than nonessential genes are charged amino acids (excluding Val), and all charged amino acids (excluding His) are more biased in essential genes.(6) Aromatic amino acids——Phe(F), Typ(W) and Tyr(Y), are all lower frequencies in essential and nonessential genes, and their usage are significantly different in the two types of genes, and all showed a preference for nonessential genes.