SV40 Vectors - It is a spherical virus with a circular, double-stranded 5243 bp chromosome, which encodes 5 proteins, viz., small-T, large-T (both early proteins), VP1, VP2 and VP3 (VP = virion protein), has an origin of replication (about 80 bp) and is complexed with histones to form chromatin.
Large-T is essential for viral replication, while VP1, VP2 and VP3 form the viral capsid. In laboratory, it is multiplied in cultured kidney cells of African green monkey. SV 40 genome has been used to develop mainly 3 types of vectors:
(1) transducing vectors,
(2) plasmid vectors and
(3) transforming vectors.