passages.id: split_4_test_1316_passage
passages.type: progene_text
passages.text: We isolated and characterized a gene from Dictyostelium discoideum , which encodes a protein of 279 amino acids ( 30.6kDa ) containing six transmembrane domains with two highly conserved motifs of asparagine-proline-alanine ( NPA ) found in the aquaporin family of water - channel proteins , although the second motif of the protein has been modified into NPV ( asparagine - proline - valine ) .