Fig. 1. Mouse ARAP3 domain organisation and generation of ARAP3 and ARAP3^SAM. (A) Diagram of mouse ARAP3 showing sterile alpha motif (SAM), pleckstrin homology (PH), ADP-ribosylation factor GTPase activating protein (ArfGAP), RhoGAP and Ras association (RA) domains (boxes) and tyrosine phosphorylation sites, Y1399 and Y1404 (YY). The percent amino acid sequence identity with human ARAP3 is indicated. (B) Top: diagram of the ARAP3 gene 5'-end showing alternative splicing (dotted line) via a cryptic splice acceptor site (CSA). Splicing is predicted to generate ARAP3 transcripts with different translation start sites (Kozak ATG) encoding ARAP3 isoforms with the N-terminal SAM domain (see A) or lacking a SAM domain (ARAP3^SAM). Coding and non-coding exons (grey and white boxes) and introns (horizontal line) are indicated. Bottom: plasmids containing cDNAs corresponding to the differentially spliced ARAP3 transcripts were transfected in 293T cells. Whole cell lysate (WCL) from transfected cells and from mouse bone marrow-derived mast cells (BMMC) were analysed by SDS-PAGE and western blotting (WB) with an anti-ARAP3 antibody.