THE 3' HALF OF THE MOUSE MAMMARY-TUMOR VIRUS ORF GENE IS NOT SUFFICIENT FOR ITS SUPERANTIGEN FUNCTION IN TRANSGENIC MICE

The Mouse Mammary Tumor Virus (MMTV) long terminal repeat contains an open reading frame (orf) of 960 nucleotides encoding a 36 kDa polypept ide with a putative transmembrane domain and five N-glycosylation site s in the N-terminal part of the protein. Transgenic mice bearing eithe r the complete or the 3' terminal half of the orf sequence of MMTV-GR under the control of the SV40 promoter were raised. As shown previousl y by FACS analysis transgenic mice which express the complete orf gene have a significant deletion of Vbeta14 expressing T cells at 6 weeks of age. Here we show that no clonal deletion of Vbeta14 bearing T cell s takes place in transgenic mice that contain orf sequences from the f ifth ATG to the termination codon. The pattern of tissues expressing t he truncated transgene was studied by the Polymerase Chain Reaction (P CR) and was very similar to the one obtained in the Vbeta14 deleting a nimals. These data suggest that the amino-terminal portion of the ORF protein (pORF) is required for a superantigen function, while our prev ious data indicated that determinants from the carboxy-terminus play a n important role for TCR Vbeta specificity.