Superantigen expression is driven by both mouse mammary tumor virus long terminal repeat-associated promoters in transgenic mice

Abstract

In addition to the usual retroviral promoter, the mouse mammary tumor virus (MMTV) long terminal repeat carries a second promoter located in the U3 region. Here we show that both of these promoters are independently able to give rise to superantigen activity in transgenic mice. The ability of multiple MMTV promoters to drive superantigen expression underscores its importance in the virus life cycle.

FIG. 1

Schematic representation of the MMTV constructs used. The plasmid pGR102 carries a hybrid provirus in which the 5′ half is from Mtv-8 and the 3′ half is from Mtv-2 (13). The Sag, encoded by the open reading frame located in the 3′ LTR (shaded box), is thus derived from the Mtv-2 provirus and specifically interacts with Vβ14-bearing T cells (2). The plasmid pORFexp was derived from pGR102 by deletion of the internal NcoI fragment. Also shown are the locations of the classic promoter (P₁₁₉₆) and other promoters present in the LTR (P₆₉₈) or in the env gene (P₇₂₄₆ and P₈₄₉₈) (nomenclature as given in reference 11). The enhancer (E_pol) shown to be important for Sag activity from P₇₂₄₆ is indicated as an open box, as are the HpaI (H), PvuII (P), and NcoI (N) restriction sites used in the construction of the plasmids pORFexp, pΔU3, and pΔRU5. At the bottom of the figure, the positions of the primers used for the PCR analysis are shown.