A guanosine ribonucleotide
(it has the nitrogenous base guanine
attached to the sugar ribose
) which has a methyl group
attached to the 7th ring atom
of the guanine
atom). These are found at the capped 5'-ends of eukaryotic mRNA
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.