Gj. Wilson et al., PERSISTENT REOVIRUS INFECTIONS OF L-CELLS SELECT MUTATIONS IN VIRAL ATTACHMENT PROTEIN SIGMA-1 THAT ALTER OLIGOMER STABILITY, Journal of virology, 70(10), 1996, pp. 6598-6606
During maintenance of L-cell cultures persistently infected with reovi
rus, mutations are selected in viruses and cells. Cells cured of persi
stent infection support growth of viruses isolated from persistently i
nfected cultures (PI viruses) significantly better than that of wild-t
ype (wt) viruses, In a previous study, the capacity of PI virus strain
WC to grow better than wt strain type 1 Lang (T1L) in cured cells was
mapped genetically to the S1 gene (R. S. Kauffman, R. Ahmed, and B. N
. Fields, Virology 131:79-87, 1983), which encodes viral attachment pr
otein sigma 1. To investigate mechanisms by: which mutations in S1 con
fer growth of PI viruses in cured cells, we determined the S1 gene nuc
leotide sequences of WC virus and six additional PI viruses isolated f
rom independent persistently infected L-cell cultures. The S1 sequence
s of these viruses contained from one to three mutations, and with the
exception of Pf 2A1, mutations in each S1 gene resulted in changes in
the deduced amino acid sequence of sigma 1 protein, Using electrophor
esis conditions that favor migration of sigma 1 oligomers, we found th
at sigma 1 proteins of L/C, PI 1A1, PI 3-1, and PI 5-1 migrated as mon
omers, whereas sigma 1 proteins of wt reovirus and PI 2A1 migrated as
oligomers, These findings suggest that mutations in sigma 1 protein af
fecting stability of sigma 1 oligomers are important for the capacity
of PI viruses to infect mutant cells selected during persistent infect
ion, Since no mutation was found in the deduced amino acid sequence of
PE 2A1 sigma 1 protein, we used T1L x PI 2A1 reassortant viruses to i
dentify viral genes associated with the capacity of this PI virus to g
row better than wt in cured cells. The capacity of PI 2A1 to grow bett
er than T1L in cured cells was mapped to the S4 gene, which encodes ou
ter-capsid protein sigma 3. This finding suggests that in some crises,
mutations in sigma 3 protein in the absence of al mutations confer gr
owth of PI viruses in mutant cells, To confirm the importance of the S
1 gene in PI virus growth in cured cells, we used T1L x PI 3-1 reassor
tant viruses to genetically map the capacity of this PI virus to grow
better than wt in cured cells, In contrast to our results using PI 2A1
, we found that growth of PI 3-1 in cured cells was determined by the
sigma 1-encoding S1 gene, Given that the sigma 1 and sigma 3 proteins
play important roles in reovirus disassembly, findings made in this st
udy suggest that stability of the viral outer capsid is an important d
eterminant of the capacity of reoviruses to adapt to host cells during
persistent infection.