The synapsin (syn) protein family comprises the neuron-specific phosphoproteins syn I, II, and III, all found in at least two isoforms (Südhof et al. 1989; Porton et al. 1999). Mature syns localize to the membrane of neurotransmitter-releasing synaptic vesicles; they are expected to have regulatory roles in linking the vesicles to the cytoskeleton, supported by the identified abilities of the syns to bind both phospholipids (Schiebler et al. 1986) and tubulin/actin (Baines and Bennett 1986; Bähler and Greengard 1987). Originating from an alternatively spliced common transcript, syn Ia is the full-length protein, whereas the isoform syn Ib holds a truncated and altered carboxy terminal. The peptide chain of syn I is divided into five domains. The common domains are designated A-D; the last and divergent domain is E in syn Ia and F in syn Ib (Südhof et al. 1989). Of these domains, A, C, and E/F show the highest degree of conservation between species and within the protein family. The central neurobiological functions of syn I are well illustrated by knock-out mice consistently found to display epilepsy (Li et al. 1995; Rosahl et al. 1995). More recently, and supportive of the mice experiments, a nonsense mutation leading to a truncated form of syn I, without domain D and E/F, was identified in a family with frequent cases of X-linked epilepsy (Garcia et al. 2004).

This study reports molecular cloning and characterization of the coding sequence of the porcine ortholog of syn I, including identification and verification at the protein level of an alanine-encoding insert