Disease relevance of MPyVgp1

• The deduced amino acid sequences for small T antigen and the part of large T antigen markedly resembled those of polyoma virus BK and simian virus 40 [1].
• The sequence probably also covers the entire coding region of two of the polyoma virus early proteins--small and middle T antigens--as well as part of the coding region for large T antigen [2].
• Defined, radiolabeled fragments of the viral genome were reacted with crude nuclear extracts prepared from lytically infected mouse 3T6 cells, and the fragments bound by large T antigen were immunoprecipitated with anti-T serum and Formalin-fixed Staphylococcus aureus [3].
• Construction of a helper-free recombinant adenovirus that expresses polyomavirus large T antigen [4].
• Ad5PyR39 replicated efficiently without a helper virus in human 293 cells and expressed hybrid mRNAs of the expected size and composition that were translated to yield large T antigen [4].

High impact information on MPyVgp1

• When added to a permeabilized cell system for nuclear import, the purified proteins increase by 2- to 3-fold the nuclear accumulation of a fluorescent protein containing the large T antigen NLS [5].
• A mutant SV40 genome carrying a frameshift at the carboxyl terminus of the large T antigen failed to replicate SV40 DNA and to transform rat2 cells, although the altered region is known to be dispensable for these functions [6].
• Analysis of plaques, obtained after transfection with SV40 DNA molecules harboring a single mispair in a defined orientation within the intron of the large T antigen gene, revealed that all types of base/base mispairs were corrected, albeit with different efficiencies and specificities [7].
• In order to investigate viral oncogenesis, we generated transgenic mice carrying either the Py large T antigen (LT) gene or the Py middle T antigen (MT) gene linked to Py early region regulatory sequences [8].
• Cells transformed by Polyoma virus (Py) can undergo a high rate of excision or amplification of integrated viral DNA sequences, and these phenomena require the presence of homology (i.e., repeats) within the viral insertion as well as a functional viral large T antigen (T-Ag) [9].

Chemical compound and disease context of MPyVgp1

• In various permissive monkey cell lines infected with simian virus 40 there are two major forms of large T antigen which differ in their rate of sedimentation through sucrose gradients [10].
• The authors have used transgenic mice to study the activity of a hybrid oncogene made up of 1.25 kb of 5' upstream sequences, derived from the bovine vasopressin gene, promoting the expression of the large T-antigen coding sequences of the early region of simian virus 40 [11].
• Polyomavirus large T antigen is phosphorylated on both serine and threonine residues at a ratio of approximately 6 to 1 [12].
• Simian virus 40 small-t and large-T antigen were synthesized in vitro and labeled with methionine donated by initiator tRNA [13].
• Guanine nucleotide contacts within viral DNA sequences bound by polyomavirus large T antigen [14].

Biological context of MPyVgp1

• Within this region consisting of 945 base pairs, we located the origin of DNA replication near 0.7 map units, the entire coding region for small T antigen, and the splice junctions for large-T-antigen mRNA [1].
• The ability to activate the viral late promoter in trans was retained by the dl1041 mutant large T-antigen, suggesting that immortalization and trans-activation of the late promoter represent two distinct activities of the protein [15].
• One of these elements, termed the core, contains an adenine-thymine-rich area, a 32-base-pair guanine-cytosine-rich palindrome, and a large T antigen binding site, and likely includes the site from which bidirectional DNA replication initiates [16].
• These begin at a site only slightly overlapping the early boundary of the core replication origin, a location highly homologous to that of simian virus 40 large T antigen-binding site I, but then extend away from the origin toward the early coding sequence and thus span the early region transcriptional initiation sites [17].
• Viable deletion mutant in the medium and large T-antigen-coding sequences of the polyoma virus genome [18].

Anatomical context of MPyVgp1

• To define the minimal cis-acting sequences required for polyomavirus DNA replication (ori), we constructed a number of polyomavirus-plasmid recombinants and measured their replicative capacity after transfection of a permissive mouse cell line capable of providing polyomavirus large T antigen in trans (MOP cells) [16].
• By these techniques, the viral large T-antigen was found almost exclusively in the nucleus, sometimes in association with nuclear pores, but never in the nucleolus [19].
• Thus, the results suggest that, for established Fischer rat fibroblasts, the maintenance of any of the three phenotypes tested and, in particular, of serum independence is not necessarily correlated with the levels of large T antigen or fragments thereof [20].
• Synthetic peptides, 2 derived from the sequence common to small, middle and large T-antigen, and I derived from the sequence unique for middle T, activated lymphocytes from polyoma-virus-immunized, but not from control mice, to release the lymphokine migration inhibitory factor (MIF) [21].
• The mutant nonkaryophilic large T antigen in NIH3T3 transformant was localized in cytoplasmic membrane fractions [22].

Associations of MPyVgp1 with chemical compounds

• In addition, the 63,000- and 20,000-dalton antigens contained two other methionine peptides absent from the large T-antigen species [23].
• These proteins had approximate molecular weights of 105,000 (large T antigen), 63,000 (middle T antigen), and 20,000 (small T antigen) as estimated by acrylamide gel electrophoresis [23].
• Two mutants, ts-25 and ts-52, have different single-base changes at the same position (2883) in the early region corresponding to a conserved glycine residue very near the C-terminus of the polyoma large T antigen [24].
• However, the prolongation of S and G2 phases in the presence of cycloheximide was not suppressed in cells expressing large T antigen, by infection with SV40 in the current generation [25].
• Whereas small T-antigen and nuclear large T-antigen were fully immunoreactive, cytoplasmic large T-antigen reacted poorly with PAb 402 or polyclonal antibodies unless the mRNP moiety was removed by treatment with EDTA/RNase A [26].

Other interactions of MPyVgp1

• Correlation with protein data suggests that one frame codes for part of middle T antigen and the other for part of large T antigen [2].

Analytical, diagnostic and therapeutic context of MPyVgp1

• To map the polyomavirus large T antigen binding sites on the viral genome we employed a quantitative immunoassay [3].
• Peptide mapping studies of the SV3T3 C120 super T-antigen were consistent with its being derived from an internally duplicated template, since the protein has methionine and cysteine tryptic fingerprints virtually identical to those of normal large T-antigen, with certain methionine peptides present in greater than one molar yield [27].
• Studies on the polyoma-virus-induced tumor-specific transplantation antigen (TSTA)--does middle or large T-antigen play a role [28]?
• As shown by immunoblotting, 125I-labeled PAb 416 was bound to a 17-kDa N-terminal fragment of large T-antigen (amino acid residues 1-130), and PAb 423 was bound to several overlapping fragments derived from the C terminus of large T-antigen [26].
• Microinjection of either mutant C6 SV40 DNA, which encodes a large T antigen unable to bind specifically to viral regulatory sequences, or deleted viral DNA lacking part of the large T antigen coding sequences yielded ratios of L-strand to E-strand RNA that were similar to those observed with wild-type SV40 DNA [29].

References