Identification and characterization of gamma-giardin and the gamma-giardin gene from Giardia lamblia.

The giardins are abundant cytoskeletal proteins that range in size from 29-38 kDa and are specific to the ventral disk of the intestinal protozoan parasite Giardia lamblia. The 29-kDa (beta and beta-1; refs. 8-10) and the 33-kDa (alpha-1 and alpha-2; refs. 3 and 7) giardins have been characterized previously. In this paper we extend the analysis of the giardins to include the 38-kDa giardin, which we have named gamma-giardin. After purifying gamma-giardin by two-dimensional electrophoresis, we raised polyclonal antibodies to the protein and used them to demonstrate that gamma-giardin shares at least one epitope with 9 other giardin polypeptides and that it localizes to the ventral disk of the parasite. We also determined an internal peptide sequence of 12 amino acid residues and used this information to construct oligonucleotide probes for the gamma-giardin gene. After cloning the gene, we determined the nucleotide sequence of its 933-bp open reading frame and 866 bp of 5' and 3' flanking sequence. We found the downstream AGTPuAAPy motif typical of all G. lamblia genes sequenced to date, and determined that the single copy of the gamma-giardin gene localizes to the same chromosome or chromosomal cluster as the alpha-giardins. Finally, we demonstrated by primer extension analysis that gamma-giardin transcripts contain a short untranslated leader characteristic of G. lamblia messenger RNAs.