Gsα is encoded by 13 exons [24], but due to alternative pre-mRNA splicing, the Gsα transcript has several variants (Fig. 2). The long and the short Gsα variants (Gsα-L and Gsα-S, respectively) differ from each other by the inclusion or exclusion of 45 nucleotides derived from exon 3 [24-26]. Nearly all tissues express both of these Gsα variants, which are typically detected as 52- and 45-kDa protein bands on Western blots. In addition, each Gsα form either includes or excludes a CAG tri-nucleotide (encoding serine) at the start of exon 4. Some investigations have revealed small, but potentially important, differences between the activities of Gsα-L and Gsα-S. For example, Gsα-L has been demonstrated to have a greater ability to transmit receptor signaling than Gsα-S when partially purified proteins from rabbit liver were examined [27], although the opposite was suggested in an assay system using cultured pancreatic islet cells [28]. Moreover, Gsα-L appears to release GDP ~2-fold faster than Gsα-S [29], and consistent with that finding, study of fusion proteins involving the β2-adrenergic receptor and either Gsα-L or Gsα-S has shown
