Figure 3.3.

Schematic diagrams of mouse Xirp2/mXinβ genomic organization and its encoded message and protein variants. The mouse Xinβ gene contains eight small exons and one large exon (E7) (McCalmon et al., 2010; Wang et al., 2010). The inclusion of E8 together with the usage of different poly(A) sites gives rise to two distinct messages, which encode exactly the same protein with 3283 amino acid residues (mXinβ) (Wang et al., 2010). On the other hand, the exclusion of E8 leads to another message, which encodes protein with 3300 amino acid residues (mXinβ-a) (Wang et al., 2010). The predicted amino acid number, molecular mass, and pI value for each mouse Xinβ protein variants are listed to the right of their respective message diagrams. Estimated from relative abundance of messages, it was predicted that mXinβ is the major variants from mouse Xinβ gene (Wang et al., 2010). At the protein level, SDS-PAGE analysis could not effectively separate these two variants. However, specific antibody U1040 generated against the very C-terminal sequence (aa#3255–3278) of mXinβ reacts only with mXinβ, whereas common antibody U1013 generated against aa#1–532 of mXinα recognizes both mXinβ and mXinβ-a (Wang et al., 2010). Similar gene organization and splicing events were also found in human XIRP2/hXinβ gene (NCBI database).