Skip to main content
. 2021 Jul 8;9:668996. doi: 10.3389/fcell.2021.668996

FIGURE 1.

FIGURE 1

Transcription initiation and translation initiation sites of BTK isoforms. (A) X chromosome map of the BTK locus. BTK-A is the isoform expressed in B-cells. BTK-C exon1 transcription initiates 255 bp from the start site of the ribosomal protein L36a gene and is the predominant form expressed in some epithelial tumor cell lines. (B) Exon1C encodes a phylogenetically conserved 34 amino acid extension at the N terminus. Translational initiation of p65BTK occurs at a conserved methionine codon in exon 3. Some sequence has been omitted from exon2 for clarity. (C) Structures of BTK isoforms with motifs shown. Activating phosphorylation sites pY223 and pY551 are shown. Cysteine at 481 is the binding site for BTK inhibitors ibrutinib, AVL-292 (spebrutinib) and acalabrutinib. p65BTK has a partial PH domain. BTK-C has a 34-amino acid extension of PH domain. BTK-D has a partially deleted kinase domain.