Dayue Chen

VCP, the mammalian homolog of cdc48, is tyrosine phosphorylated in response to T cell antigen receptor activation.

Activation of T cells through the T cell antigen receptor (TCR) results in the rapid tyrosine phosphorylation of a number of cellular proteins, one of the earliest being a 100 kDa protein. We have sought to identify this 100 kDa substrate by partially purifying the protein by antiphosphotyrosine (APT) affinity purification, in order to obtain amino acid sequence data and, using this information, to isolate the cDNA clone encoding the molecule. We report here that the amino acid sequence data showed pp100 to be the murine equivalent of porcine valosin containing protein (VCP), a finding confirmed from the cloning and sequencing of the murine pp100 cDNA. Sequence analysis has shown VCP to be a member of a family of ATP binding, homo‐oligomeric proteins, and the mammalian homolog of Saccharomyces cerevisiae cdc48p, a protein essential to the completion of mitosis in yeast. We also provide proof that both endogenous and expressed murine VCP are tyrosine phosphorylated in response to T cell activation. Thus we have identified a novel component of the TCR mediated tyrosine kinase activation pathway that may provide a link between TCR ligation and cell cycle control.

Effect of Intragenic Rearrangement and Changes in the 3′ Consensus Sequence on NSP1 Expression and Rotavirus Replication

ABSTRACT The nonpolyadenylated mRNAs of rotavirus are templates for the synthesis of protein and the segmented double-stranded RNA (dsRNA) genome. During serial passage of simian SA11 rotaviruses in cell culture, two variants emerged with gene 5 dsRNAs containing large (1.1 and 0.5 kb) sequence duplications within the open reading frame (ORF) for NSP1. Due to the sequence rearrangements, both variants encoded only C-truncated forms of NSP1. Comparison of these and other variants encoding defective NSP1 with their corresponding wild-type viruses indicated that the inability to encode authentic NSP1 results in a small-plaque phenotype. Thus, although nonessential, NSP1 probably plays an active role in rotavirus replication in cell culture. In determining the sequences of the gene 5 dsRNAs of the SA11 variants and wild-type viruses, it was unexpectedly found that their 3′ termini ended with 5′-UGAACC-3′ instead of the 3′ consensus sequence 5′-UGACC-3′, which is present on the mRNAs of nearly all other group A rotaviruses. Cell-free assays indicated that the A insertion into the 3′ consensus sequence interfered with its ability to promote dsRNA synthesis and to function as a translation enhancer. The results provide evidence that the 3′ consensus sequence of the gene 5 dsRNAs of SA11 rotaviruses has undergone a mutation causing it to operate suboptimally in RNA replication and in the expression of NSP1 during the virus life cycle. Indeed, just as rotavirus variants which encode defective NSP1 appear to have a selective advantage over those encoding wild-type NSP1 in cell culture, it may be that the atypical 3′ end of SA11 gene 5 has been selected for because it promotes the expression of lower levels of NSP1 than the 3′ consensus sequence.

Cell‐line‐induced mutation of the rotavirus genome alters expression of an IRF3‐interacting protein

Rotavirus, a cause of severe gastroenteritis, contains a segmented double‐stranded (ds)RNA genome that replicates using viral mRNAs as templates. The highly conserved 3′‐consensus sequence (3′CS), UGUGACC, of the mRNAs promotes dsRNA synthesis and enhances translation. We have found that the 3′CS of the gene (g5) encoding NSP1, an antagonist of interferon signaling, undergoes rapid mutation when rhesus rotavirus (RRV) is serially passaged at high multiplicity of infection (MOI) in cells permitting high titer growth. These mutations increase the promoter activity of the g5 3′‐sequence, but decrease its activity as a translation enhancer. The location of the mutations defines the minimal essential promoter for dsRNA synthesis as URN0–5CC. Under passage conditions where cell‐to‐cell spread of the virus is required to complete infection (low MOI), the 3′CS is retained due to the need for NSP1 to be expressed at levels sufficient to prevent establishment of the antiviral state. These data demonstrate that host cell type and propagation conditions affect the capacity of RRV to produce the virulence gene product NSP1, an important consideration in producing RRV‐based vaccines.