Figure 2.

(A) Sequence of BAP-135. The nucleotide sequence is shown on the upper line; the deduced amino acid sequence is shown on the lower line. Sequences of tryptic peptides used to identify BAP-135 cDNA are underlined. (B) Identification of a repetitive amino acid motif in BAP-135. The BAP-135 amino acid sequence is diagrammed (Upper). The 95-residue repeat unit (hatched boxes), sequences homologous to the Src autophosphorylation site (open boxes), and regions of unique sequence (solid boxes) are indicated. Numbers refer to amino acid residues at the boundaries of repeat units. Amino acid sequences of the individual repeats are compared (Lower). Residues are numbered at left and right; amino acid identities, with reference to the second repeat (residues 304–398), are shaded. A consensus sequence (core) was derived by comparison of the four full-length repeats (residues 304–398, 409–503, 514–608, and 676–770). (C) BAP-135 is associated with Btk in B cells. Immunoprecipitation from lysates of pervanadate-stimulated (lanes 6–10) or unstimulated (lanes 1–5) RAMOS cells was performed using anti-Btk antibodies (Ab1280, lanes 2 and 7; Ab1300, lanes 4 and 9), preimmune sera (lanes 1, 3, 6, and 8), or rabbit IgG (lanes 5 and 10). BAP-135 (Upper) was detected by immunoblotting with Ab2240; Btk (Lower) was detected with Ab1280. Epitope-tagged (lane 12) and untagged (lane 13) BAP-135 coding sequences were transferred to the expression vector pCIS-2 and expressed in 293 cells by transient transfection; BAP-135 was detected in total lysates of untransfected (lane 11) and transfected cells by immunoblotting.