Modified nucleosides and bizarre 5'-termini in mouse myeloma mRNA.

Messenger RNAs from mouse myeloma cells contain N-6-methyl adenosine and novel 5' termini having 7-methy-guanosine in a 5', 5' triphosphate linkage with ribose-methylated nucleosides. Ten common 5'-terminal sequences of the forms m-7-G-5'-PPP-5'-NmpNp and m-7-G-5'-ppp-5'-NmpNmpNp are reported. Structures like this may be a general feature of mRNA in eukaryotes.