AI Article Synopsis

  • The vaccinia virus J3 protein has three key roles in mRNA synthesis and modification: it acts as a methyltransferase, a processivity factor for poly(A) polymerase, and a positive transcription elongation factor during gene expression.
  • Experiments reveal that the methyltransferase and poly(A) polymerase functions can be genetically separated, indicating that they operate independently.
  • Recent studies show that the positive transcription elongation activity of J3 is also an independent function and that neither the poly(A) polymerase nor the methyltransferase activities are essential for the virus's growth in cell culture.

Article Abstract

Previous genetic and biochemical experiments have shown that the vaccinia virus J3 protein has three different roles in mRNA synthesis and modification. First, J3 is a (nucleoside-2'-O-)methyltransferase which methylates the 2' position of the first transcribed nucleotide, thus converting a cap-0 to a cap-1 structure at the 5' ends of mRNAs. Second, J3 is a processivity factor for the virus coded poly(A) polymerase. Third, J3 has recently been shown to have intermediate and late gene positive transcription elongation factor activity in vivo. Previous experiments have shown that the poly(A) polymerase stimulatory activity and the (nucleoside-2'-O-)methyltransferase activity are two independent functions of the protein that can be genetically separated through site-directed mutagenesis. In this article, the relationship between the J3-mediated transcription elongation activity and the two other functions of the protein was investigated by constructing several site-directed mutant viruses that contain specific defects in either methyltransferase or poly(A) polymerase processivity functions. The results demonstrate that the J3 positive transcription elongation factor activity is a third independent function of the protein that is genetically separable from its two other functions in mRNA modification. The results also show that neither the poly(A) polymerase stimulatory nor the methyltransferase activities of the J3 protein is essential for virus growth in cell culture.

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http://dx.doi.org/10.1006/viro.2002.1538DOI Listing

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