As illustrated in Fig. (3A), XLαs has several different variants. Similar to Gsα, it uses exon 3 alternatively, thus having at least a long and a short variant. In addition, analogous to Gsα-N1, a C-terminally truncated XLαs variant, termed XLαs-N1, also exists. Human XLαs-N1 appears to have a subvariant produced by inclusion of sequences from two additional exons, A20 and A21, located immediately following exon XL [36]. A similar subvariant has also been demonstrated for rat XLαs-N1 [66]. The introduction of these additional sequences into XLαs-N1 results in a frame-shift, leading to a putative protein with partial identity to XLαs but not to Gsα. Functional significance of XLαs-N1 and its variants remains unknown.
