Relation Between Gene Length And Functionality In Prokaryotes

Due to the important role of essential genes in the survival of any organism, such genes had been seen as the key to life activities. Through analysis of ten set of prokaryote genome data, we found that although the number of genes on leading strand was greater than lagging strand, however, when compared the essential genes to non-essential genes, the result showed that essential genes of three kinds of microorganisms did not show more preference than non-essential genes for the leading strand.Then, we used Escherichia coli as an example and divided its whole genome by four COG main categories and 25 COG subcategories. We found that only subcategory J and M, and main category I and II had essential genes that showed a significant difference in its preference for leading strand compared to non-essential genes. This result fitted partially with conclusions of other researchers, which implied that essential genes that had preferences for leading strand had functional specificity and species specificity.Next, we analyzed the length of E. coli essential genes. The result showed that both essential genes and non-essential genes didn’t exhibit any length difference between leading and lagging strand. However, on both leading and lagging strand an obvious length difference was found between essential and non-essential genes. After extending the analysis to all the genes of E. coli and ten prokaryotes genomes, we found that on genome level, in addition to E. coli, H. pylori and three other prokaryotes all showed different forms of length difference between essential and non-essential genes. After further detailed analysis of this phenomenon, we found that although the significant difference on the length was widespread, it differed among species and functional categories. Only genes from COG J, K and L showed a unanimous length difference. And in COG J, K, L and O, essential genes showed a larger dispersion of gene length than non-essential genes.We speculated that the differences among species and functional categories were likely to be the results of different types of natural selection in the process of evolution. The changes in both gene length and dispersion of gene length could result in increases of both diversity of genomes and adaptability of species.