The structure of the 5' terminal cap of the respiratory syncytial virus mRNA.

The 5' terminal cap structure of the mRNAs of human respiratory syncytial virus synthesized in vitro in the presence of S-adenosyl-L-methionine consists of a 7-methyl guanosine linked to an unmethylated guanosine through a 5'-5' pyrophosphate linkage formed by using the alpha and beta phosphates of GTP. The complete cap structure is m7G (5')ppp(5')Gp ... which is devoid of ribose 2'-O-methylation. Capping, including methylation, is coupled to transcription. These results constitute the first report of a pneumoviral mRNA cap structure.