Question

Please indicate how a small metabolite such as Guanine can modulate the expression of genes for the biosynthesis of purines

Answer 1

Nucleotide synthesis is an energy intensive process that uses multiple metabolic pathways across different cell compartments and several sources of carbon and nitrogen. The processes are regulated at the transcription level by a set of master transcription factors but also at the enzyme level by allosteric regulation and feedback inhibition. Riboswitches are structured noncoding RNA elements located in the 5′ untranslated regions (5′-UTR) of a mRNA molecule. Riboswitches consist of a small-molecule-binding aptamer and an expression platform that together control gene expression in cis by directly binding to small molecules. Guanine act as transcriptional regulator in biosynthesis of purine. In this end product that is guanine is a negative regulator for biosynthesis of purine. Guanine act as ligand.it bind to aptamer domain lead to conformational change. Guanine binding to its cognate riboswitch cause transcriptional attenuation by formation of an intrinsic terminator. Thus elevated cellular concentration of guanine shut down the expression of guanine biosynthesis.