Cl. Rowe et al., GENERATION OF CORONAVIRUS SPIKE DELETION VARIANTS BY HIGH-FREQUENCY RECOMBINATION AT REGIONS OF PREDICTED RNA SECONDARY STRUCTURE, Journal of virology, 71(8), 1997, pp. 6183-6190
Coronavirus RNA evolves in the central nervous systems (CNS) of mice d
uring persistent infection. This evolution can be monitored by detecti
on of a viral quasispecies of spike deletion variants (SDVs) (C. L. Ro
we, S. C. Baker, M. J. Nathan, and J. O. Fleming, J. Virol. 71:2959-29
69, 1997). We and others have Pound that the deletions cluster in the
region from 1,200 to 1,800 nucleotides from the 5' end of the spike ge
ne sequence, termed the ''hypervariable'' region. To address how SDVs
might arise, we generated the predicted folding structures of the posi
tive- and negative-strand senses of the entire 4,139-nt spike RNA sequ
ence. We found that a prominent, isolated stem-loop structure is coinc
ident with the hypervariable region in each structure, To determine if
this predicted stem-loop is a ''hot spot'' for RNA recombination, Re
assessed whether this region of the spike is more frequently deleted t
han three other selected regions of the spike sequence in a population
of viral sequences isolated from the CNS of acutely and persistently
infected mice. Using differential colony hybridization of cloned spike
reverse transcription-PCR products, we detected SDVs in which the hot
spot was deleted but did not detect SDVs in which other regions of th
e spike sequence were exclusively deleted. Furthermore, sequence analy
sis and mapping of the crossover sites of 25 distinct patterns of SDVs
showed that the majority of crossover sites clustered to two regions
at the base of the isolated stem-loop, which we designated as high-fre
quency recombination sites 1 and 2. Interestingly, the majority of the
left and right crossover sites of the SDVs were directly across from
or proximal to one another, suggesting that these SDVs are likely gene
rated by intramolecular recombination. Overall, our results are consis
tent with there being an important role for the spike RNA secondary st
ructure as a contributing factor in the generation of SDVs during pers
istent infection.