Synthesis of a fluorescent 7-methylguanosine analog and a fluorescence spectroscopic study of its reaction with wheatgerm cap binding proteins.

In the initiation of protein synthesis, the mRNA 5'-terminal 7-methylguanosine cap structure and several recognition proteins play a pivotal role. For the study of this cap binding reaction, one approach is to use fluorescence spectroscopy. A ribose diol-modified fluorescent cap analog, anthraniloyl-m7GTP (Ant-m7GTP), was designed and synthesized for this purpose. This fluorescent cap analog was found to have a high quantum yield, resistance to photobleaching and avoided overlap of excitation and emission wavelengths with those of proteins. The binding of Ant-m7GTP with wheatgerm initiation factors elF-4F and elF-(iso)4F was determined. The fluorescent cap analog and m7GTP had similar interactions with both cap binding proteins. Fluorescence quenching experiments showed that the microenvironment of Ant-m7GTP when bound to protein was hydrophobic.