Identification and characterization of SRS1, a Toxoplasma gondii surface antigen upstream of and related to SAG1

Mol Biochem Parasitol. 1997 Nov;89(2):271-82. doi: 10.1016/s0166-6851(97)00126-6.


Previous investigations of the major surface antigen (SAG1) promoter of Toxoplasma gondii indicated an ability to function bi-directionally in transient transformation assays at least. This suggests there might be another tachyzoite-specific gene being divergently transcribed from the SAG1 promoter in its normal chromosomal location. To investigate this possibility we have characterized the region upstream of SAG1 and report here a co-directional transcription unit coding for a probable GPI-anchored surface protein with homology to SAG1 and SAG3. This antigen, which had not previously been identified in surface iodination experiments is given the acronym SRS1, for SAG1-related sequence 1. Genomic organization and sequence of a full-length cDNA of SRS1 are presented. Antisera against a recombinant SRS1 protein produced in Escherichia coli, recognize a specific band of 46 kDa in parasite lysates which corresponds to the largest of the GPI-anchored proteins by Western blot. The possible role of this previously unidentified surface antigen is discussed.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antibodies, Protozoan
  • Antigens, Protozoan / analysis
  • Antigens, Protozoan / chemistry
  • Antigens, Protozoan / genetics*
  • Antigens, Surface / analysis
  • Antigens, Surface / chemistry
  • Antigens, Surface / genetics*
  • Base Sequence
  • DNA, Complementary / genetics
  • DNA, Protozoan / genetics
  • Membrane Glycoproteins / genetics
  • Molecular Sequence Data
  • Promoter Regions, Genetic / genetics
  • Protozoan Proteins / genetics*
  • RNA, Messenger / genetics
  • RNA, Protozoan / genetics
  • Recombinant Fusion Proteins
  • Sequence Analysis, DNA
  • Sequence Homology, Amino Acid
  • Toxoplasma / genetics
  • Toxoplasma / immunology*
  • Transcription, Genetic / genetics


  • Antibodies, Protozoan
  • Antigens, Protozoan
  • Antigens, Surface
  • DNA, Complementary
  • DNA, Protozoan
  • Membrane Glycoproteins
  • Protozoan Proteins
  • RNA, Messenger
  • RNA, Protozoan
  • Recombinant Fusion Proteins
  • SAG1 antigen, Toxoplasma
  • SAG3 protein, Toxoplasma gondii
  • SRS1 protein, Toxoplasma gondii

Associated data

  • GENBANK/U77677