THE SIMIAN-VIRUS-40 PACKAGING SIGNAL SES IS COMPOSED OF REDUNDANT DNAELEMENTS WHICH ARE PARTLY INTERCHANGEABLE

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 w as previously found to play a role in facilitating the nucleosomal rea rrangement required for chromatin condensation and viral packaging. He re, the fine structure of ses was investigated by genetic studies. Ana lyses of ses' revertants indicated that in order to function, ses must be present in close proximity to the origin of replication (ori), sup porting a role in the regulation of the viral life cycle. Fine dissect ion of ses was performed using a series of plasmids carrying mutations and deletions in this region. The results suggest that multiple DNA e lements participate in the SV40 packaging process, including the GC-bo xes 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 bindin g of Sp1 and/or AP-2 may participate in the packaging process. (C) 199 6 Academic Press Limited.