Detection in HeLa cell extracts of a 7-methyl guanosine specific enzyme activity that cleaves m7GpppNm.

Extracts prepared from HeLa cells contain an enzymatic activity which cleaves m7G(5')ppp(5')Gm to m7pG and ppGm. The activity exhibits a high degree of substrate specificity and does not cleave G(5')ppp(5')G or the ring opened derivative of m7GpppGm which has lost the positive charge from the N7 position of m7G. m7GpppGm as the 5' terminal structure of intact reovirus mRNA is resistant to attack by the pyrophosphatase activity, but becomes partially sensitive in the 5' terminal fragment consisting of 7-10 nucleotides derived from the same mRNA by T1 RNAase digestion. m7G(5')ppp(5')GmpCp is completely sensitive to cleavage resulting in the release of m7pG without generation of m7GpppGm as an intermediate. These results establish the existence of a 7-methyl guanosine specific pyrophosphatase activity in HeLa cells.