SV40 Large T

SV40 large T antigen (Simian Vacuolating Virus 40 TAg) is a hexamer protein that is a dominant-acting oncoprotein derived from the polyomavirus SV40. TAg is capable of inducing malignant transformation of a variety of cell types. The transforming activity of TAg is due in large part to its perturbation of the retinoblastoma (pRb) and p53 tumor suppressor proteins. In addition, TAg binds to several other cellular factors, including the transcriptional co-activators p300 and CBP, which may contribute to its transformation function.

Simian virus 40 large T antigen

Isoform large T antigen is a key early protein essential for both driving viral replication and inducing cellular transformation. Plays a role in viral genome replication by driving entry of quiescent cells into the cell cycle and by autoregulating the synthesis of viral early mRNA. Displays highly oncogenic activities by corrupting the host cellular checkpoint mechanisms that guard cell division and the transcription, replication, and repair of DNA. Participates in the modulation of cellular gene expression preceeding viral DNA replication. This step involves binding to host key cell cycle regulators retinoblastoma protein RB1/pRb and TP53. Induces the disassembly of host E2F1 transcription factors from RB1, thus promoting transcriptional activation of E2F1-regulated S-phase genes. Inhibits host TP53 binding to DNA, abrogating the ability of TP53 to stimulate gene expression. Plays the role of a TFIID-associated factor (TAF) in transcription initiation for all three RNA polymerases, by stabilizing the TBP-TFIIA complex on promoters. Initiates viral DNA replication and unwinding via interactions with the viral origin of replication. Binds two adjacent sites in the SV40 origin. The replication fork movement is facilitated by Large T antigen helicase activity. Activates the transcription of viral late mRNA, through host TBP and TFIIA stabilization. Interferes with histone deacetylation mediated by HDAC1, leading to activation of transcription. May inactivate the growth-suppressing properties of the E3 ubiquitin ligase CUL7.
Isoform 17kT antigen targets host RBL2 for degradation and promotes cell proliferation. Transactivates host cyclin A promoter through its J domain.

Biological Process bidirectional double-stranded viral DNA replicationManual Assertion Based On ExperimentIDA:UniProtKB
Biological Process DNA unwinding involved in DNA replicationManual Assertion Based On ExperimentIDA:UniProtKB
Biological Process modulation by virus of host G1/S transition checkpointIEA:UniProtKB-KW
Biological Process modulation by virus of host protein ubiquitinationIEA:UniProtKB-KW
Biological Process modulation by virus of host ubiquitin-protein ligase activityIEA:UniProtKB-KW
Biological Process suppression by virus of host JAK-STAT cascade via inhibition of JAK1 activityIEA:UniProtKB-KW
Biological Process suppression by virus of host type I interferon-mediated signaling pathwayIEA:UniProtKB-KW
Biological Process viral DNA genome replicationManual Assertion Based On ExperimentIDA:UniProtKB

Host nucleus

Phosphorylated on both serine and threonine residues. Phosphorylation on Ser-120 and Ser-123 inhibits viral replication, while phosphorylation on Thr-124 enhances replication by activating the DNA-binding domain. Phosphorylation on Thr-701 is required for binding to host FBW7gamma isoform. Dephosphorylated preferentially by PP2A on Ser-120, Ser-123, Ser-677 and perhaps Ser-679. Small t antigen inhibits the dephosphorylation by the AC form of PP2A.
O-Glycosylated near the C-terminal region.
Acetylated by CBP in a TP53-dependent manner.