Nontemplated bases at the 5′ ends of tacaribe virus mRNAs

Centrifugation of Tacaribe arenavirus-infected cell extracts on CsCl density gradients was used to separate genomes and antigenomes, which band at 1.31 g/ml as nucleocapsids, from mRNAs which pellet. Primer extensions on the banded RNAs showed that the Fends of the genomes and antigenomes were unique, whereas primer extensions on the mRNAs showed that their 5′ ends were heterogenous in length, extending 0–4 bases beyond the 3′ ends of the templates for their synthesis. This suggests that arenavirus mRNAs may initiate by a cap-snatching mechanism, some-what similar to influenza viruses and bunyaviruses. We also found an extra G residue at the Fend of the genome RNA, which was not predicted according to current models. This is now the third time that the unexpected G residue has been found at the Fend of arenavirus genomes.