The recombinant plasmid p102 based on pBR322 carrying -50% of the replicator proximal early region of simian virus 40 (SV40) DNA, including the viral origin of replication, has been constructed. It lacks a major part of the large tumor (T) antigen 3'-coding region, the T-antigen termination codon, and the polyadenylylation site. The plasmid was transferred together with the herpes simplex virus thymidine kinase (TK) gene as a selectable marker to mouse LTK-cells. TKV cell clones were isolated and their high molecular weight DNAs were shown by DNA blotting and hybridization experiments to contain the SV40 DNA fragment from the recombinant. In some of these clones, heterogeneous expression of the SV40 DNA fragment could be detected by immunofluorescence while, in control experiments in which a plasmid containing the complete SV40 early DNA region was used, this extensive heterogeneity of T-antigen expression was not observed. RNA-DNA hybridization experiments showed that the SV40-specific RNA of those clones is polyadenylylated. The molecular weight of the T-antigen-related protein coded by p102 corresponded well to the expected coding capacity of the SV40 DNA fragment. Small tumor antigen was not expressed.The small DNA tumor virus simian virus 40 (SV40) codes for two early proteins: large tumor (T) antigen (Mr, =96,000) and small tumor (t) antigen (Mr~z20,000). Possible functions of t antigen in viral replication and transformation have not yet been elucidated, but multiple and diverse functions in both events have been inferred for SV40 T antigen (1). SV40 T antigen, therefore, seems to be a pleiotropic molecule (2). Studies with adenovirus serotype 2-SV40 hybrids have shown that certain functions can be performed by COOH-terminal fragments of T antigen, indicating that T antigen contains a variety of functional domains (3). Whereas analysis of adenovirus 2-SV40 hybrids has allowed the characterization of some biological properties ofthe COOH-terminal domains of SV40 T antigen, so far little is known about its NH2-terminal domains. Recent data, however, suggested that the 5'-coding region of T antigen may be involved in its transformation functions but that its lytic functions require in addition the 3'-coding region (4, 5). Therefore, it seems possible that cellular transformation by SV40 might be achieved, at least in part, by NH2-terminal fragments of this molecule. However, all SV40-transformed cells analyzed so far seem to contain all sequences of the SV40 early genome region (6) and express T antigen or related molecules containing duplications of certain T-antigen sequences (super T antigen). In addition, some SV40-transformed cells express truncated T-antigen molecules.A prerequisite for studying potential functions of NH2-terminal T-antigen fragments is the expression of such fragments in the absence of functional T antigen. This might be achieved by constructing a recombinant plasmid containing NH2-terminal coding sequences of T antigen and analyzing their expression after transfection and st...
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