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J. Virol., 05 1997, 3375-3384, Vol 71, No. 5
SI Schmid and P Hearing
Selectivity and polarity of adenovirus type 5 DNA packaging are believed to
be directed by an interaction of putative packaging factors with the
cis-acting adenovirus packaging domain located within the genomic left end
(nucleotides 194 to 380). In previous studies, this packaging domain was
mutationally dissected into at least seven functional elements called A
repeats. These elements, albeit redundant in function, exhibit differences
in the ability to support viral packaging, with elements I, II, V, and VI
as the most critical repeats. Viral packaging was shown to be sensitive to
spatial changes between individual A repeats. To study the importance of
spatial constraints in more detail, we performed site-directed mutagenesis
of the 21-bp linker regions separating A repeats I and II, as well as A
repeats V and VI. The results of our mutational analysis reveal previously
unrecognized sequences that are critical for DNA encapsidation in vivo. On
the basis of these results, we present a more complex consensus motif for
the adenovirus packaging elements which is bipartite in structure. DNA
encapsidation is compromised by changes in spacing between the two
conserved parts of the consensus motif, rather than between different A
repeats. Genetic evidence implicating packaging elements as independent
units in viral DNA packaging is derived from the selection of revertants
from a packaging-deficient adenovirus: multimerization of packaging repeats
is sufficient for the evolution of packaging- competent viruses. Finally,
we identify minimally sized segments of the adenovirus packaging domain
that can confer viability and packaging activity to viruses carrying gross
truncations within their left-end sequences. Coinfection experiments using
the revertant as well as the minimal-packaging-domain mutant viruses
strengthen existing arguments for the involvement of limiting, trans-acting
components in viral DNA packaging.
Copyright © 1997, American Society for Microbiology
Bipartite structure and functional independence of adenovirus type 5 packaging elements
Department of Molecular Genetics and Microbiology, State University of New York at Stony Brook, 11794, USA.
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