m(7)G5'ppp5'm(2')AACA-mRNA(5-)
m(7)g5'ppp5'm(2')aaca-mrna(5-)
A 7-methyl guanosine (m7G) linked via an inverted 5'-5' triphosphate bridge to an initiating 2'-<em>O</em>-methyl-AACA oligonucleotide; major species at pH 7.3.