Methylated cap formation by enzymes bound to nuclear informofer particles

Abstract

Rat liver nuclear 30 S ribonucleoprotein particles containing pre-mRNA and nuclear sap proteins have been shown to modify in vitro the synthetic dinucleotide ppGpC in the presence of GTP and S-adenosyl-L-methionine (SAM) by the formation of a blocked and methylated (capped) structure 7meG(5′)ppp(5′)-G^{m e}pC. In the absence of SAM the predominant reaction product was GpppGpC. Our results indicate that the 30S ribonucleoprotein particles (informofers) as well as the proteins of the nuclear sap possess both guanylyltransferase, N⁷-, and 2-o-methyltransferase activities.