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  • Title: The simian virus 40 packaging signal ses is composed of redundant DNA elements which are partly interchangeable.
    Author: Dalyot-Herman N, Ben-nun-Shaul O, Gordon-Shaag A, Oppenheim A.
    Journal: J Mol Biol; 1996 May 31; 259(1):69-80. PubMed ID: 8648649.
    Abstract:
    Using the experimental system of simian virus 40 (SV40) pseudovirions we have previously shown that SV40 requires a specific DNA element for packaging, ses, which was mapped to the SV40 regulatory region. ses was previously found to play a role in facilitating the nucleosomal rearrangement required for chromatin condensation and viral packaging. Here, the fine structure of ses was investigated by genetic studies. Analyses of ses+ revertants indicated that in order to function, ses must be present in close proximity to the origin of replication (ori), supporting a role in the regulation of the viral life cycle. Fine dissection of ses was performed using a series of plasmids carrying mutations and deletions in this region. The results suggest that multiple DNA elements participate in the SV40 packaging process, including the GC-boxes and elements derived from the enhancer. The elements are redundant, and they can function in various combinations. Packaging efficiency correlated with the number of GC-boxes, known to bind Sp1. In addition, AP-2 binding elements appeared to more important than others. These findings were supported by experiments which showed that packaging was significantly enhanced by adding AP-2 binding sites to plasmids with large deletions and lacking those sites. The results imply that binding of Sp1 and/or AP-2 may participate in the packaging process.
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