Chapter 12 - Molecular mechanisms that have made bidirectional gene promoters

Abstract

In the previous chapter, we reviewed how most of the human genome is noncoding. Only 1.5% of the genome has information for amino acid sequences of biologically significant proteins. The integration of the transposable elements, which make up 45% of the human genome, should be considered for explaining the processes that might have contributed to determining the organization of genes. Some of them are head-head linked, some are tail-head linked, and some are isolated from others. Many of the human mitochondrial function-associated genes are head-head linked with other genes. We might recall that non-coding RNAs, including tRNAs, rRNAs, and a considerably large number of the lncRNAs and miRNAs are transcribed under the control of the bidirectional promoters. Although transposing activities are not so strong in human genomes, many retrotransposons and non-retrotransposons have been identified and characterized in human genomes, but they are presently almost unfunctional and seem to be merely fossils in the genome. In this chapter, we will discuss a mechanism(s) that contributed to the integration of the mitochondrial ancestral genes into eukaryotic cells. Then, we will be able to discuss the possible reasons, and the molecular mechanisms, that made the bidirectional promoters in human genomes.