Yeast TOR (DRR) proteins: amino-acid sequence alignment and identification of structural motifs.

The yeast TOR1 (DRR1) and TOR2 (DRR2) proteins are putative targets of the immunosuppressive drug rapamycin (Rm), defined by dominant drug-resistance mutations. They share a large C-terminal domain that exhibits sequence similarity to the 110-kDa subunit of phosphatidylinositol (PI) 3-kinases. In this report, we present an amino acid (aa) sequence alignment of TOR1 (DRR1) and TOR2 (DRR2) and identify conserved and nonconserved motifs within the N-terminal domain that are indicative of possible nuclear localization. We also show that the mutations responsible for Rm resistance in four independent drr2dom alleles alter the identical aa (Ser1975-->Arg) previously identified in drr1dom mutants (Ser1972-->Arg or Asn). Models for TOR (DRR) protein function are discussed.