Modulation of replication, aminoacylation and adenylation in vitro and infectivity in vivo of BMV RNAs containing deletions within the multifunctional 3′ end.

The genome of brome mosaic virus (BMV) is comprised of three (+) strand RNAs, each containing a similar, highly structured, 200 base long sequence at its 3′ end. A 134 base subset of this sequence contains signals directing interaction of the viral RNA with BMV RNA replicase, ATP,CTP:tRNA nucleotidyl transferase and aminoacyl tRNA synthetase. A series of mutants containing deletions within this region, previously constructed and tested in vitro for the effect on replication and aminoacylation activities, has now been assayed in vitro for adenylation function and in vivo for ability to replicate in isolated protoplasts and whole plants. These tests indicate that features of viral RNA recognized by BMV replicase overlap those directing adenylation, but are distinct from those directing aminoacylation. Consequently, the lethality of a deletion preferentially inhibiting aminoacylation suggests that this function may have an essential role contributing to viral replication in vivo. An RNA3 mutant bearing a 20‐base deletion yielding normal levels of aminoacylation and enhanced levels of replicase template activity and adenylation in vitro was able to replicate in protoplasts and plants; however, its accumulation in protoplasts was reduced relative to wild‐type. This suggests that additional functions affecting the replication and accumulation of viral RNA reside in the conserved 3′ sequence.