Truncations and site-directed mutagenesis in the carboxyl terminus and 3i loop of CXCR3. (A) Carboxyl terminus alignment of CXCR1, CXCR2, CXCR3, and CXCR4. (B) 3i loop subdomain of CXCR1, CXCR2, CXCR3, and CXCR4. (C) CXCR3 carboxyl-terminus. The carboxyl-terminal truncations of CXCR3 were generated by introducing stop codons (*) at Ser349, Leu332, or Glu327. 332-334L→A site-directed mutagenesis was generated as described in “Materials and methods.” (D) CXCR3 3i loop subdomain. Site-directed mutagenesis at position 245, replacing serine with alanine, was generated as described in “Materials and methods.” Serine and threonine residues that serve as potential phosphorylation sites are underlined, and the leucine motifs are in bold. The site-directed mutagenesis is in bold italics. Positions are indicated according to Feature Aligner of ExPASy, Swiss-Prot (Swiss Institute of Bioinformatics, Basel, Switzerland).