Abstract
Inosine 5’-monophosphate dehydrogenase (IMPDH) is a purine biosynthetic enzyme that catalyzes oxidation of inosine monophosphate (IMP) to xanthosine monophosphate (XMP). This enzyme is a homotetramer, and each monomer is composed of a catalytic domain and a subdomain with two Cystathionine β-synthase (CBS) domains. The deletion of CBS domain does not affect the catalytic function of IMPDH. In previous study, IMPDH was shown to bind to DNA to function as transcription repressor in Drosophila cells. In my study, IMPDH was shown to form two complexes were found in pulled down IMPDH separately, They are RNA polymerase and ribosome in Escherichia coli. IMPDH was isolated by IMP column, and then results were presented on Western Blotting. We discovered that the connection links IMPDH to these proteins is non-covalent bond. When E. coli culture was treated with a gyrase inhibitor, the RNA polymerase band was absent in Western Blotting result in pulled down IMPDH, which indicates DNA unwinding process is the step that the IMPDH- RNA polymerase complex is formed. While when we inhibited transcription, translation and DNA unwinding process of E. coli separately, ribosome bands were shown in all pulled down IMPDH. Therefore, in which step ribosome forming complex to IMPDH is still unknown right now. Because the guanine nucleotide pool is controlled by IMPDH, so when the \r excessive of guanine was added to cell culture, the forming of IMPDH- RNA polymerase complex was increased, while the forming of IMPDH- ribosome complex was decreased. This result will give us a hint that guanine will lead IMPDH devote more to form complexes with RNA polymerase and less IMPDH will bind to ribosome. The binding site of IMPDH to ribosome is located. Ribosome 30S band is shown in pulled down IMPDH with ΔCBS. This result indicates that ribosome interacts to IMPDH through the catalytic domain.