Both genomic and cDNA clones have been isolated encoding the major sheath glycoprotein, gp22, of Litomosoides carinii microfilariae. The mature gp22 mRNA is shown to result from both trans-splicing of a 22-nucleotide 5'-leader sequence to an acceptor site at position 313 of the pre-mRNA, immediately upstream from the start codon, and from cis-splicing of a 117-nt intron located within the coding sequence. Cis-splicing precedes the trans-splicing reaction. The gp22 reading frame of 148 codons has the inferred structure of a prepro-protein and includes a leader peptide and a pro-segment ahead of the known N terminus of the mature, extracellular protein of 105 amino acids. The N-terminal part of that protein contains five repeats of an elastin-related pentapeptide sequence, which, together with a proline-threonine segment between two Cys clusters in the center and at its C terminus, may cause an elongated conformation with an apparent molecular size of 22 kDa in contrast to the calculated M(r) of 11,200.