A structure-function analysis of NOD, a kinesin-like protein from Drosophila melanogaster.

We have analyzed a collection of 12 mutations in the Drosophila melanogaster nod locus, which encodes a kinesin-like protein involved in female meiotic chromosome segregation. The kinesin-like domain is at the N-terminus of the protein, while the C-terminal portion of the protein is unique. Four of the mutations are missense and affect highly conserved domains of the kinesin-like portion of the predicted protein, and thus demonstrate that the sequence conservation is biologically relevant. Surprisingly, two other mutations, which behave genetically as null alleles, are the result of mutations in the last exon of the nod gene. Thus, these two mutations affect the most C-terminal residues in the unique portion of the predicted protein. Based on these mutations, we suggest that this part of the protein may also be essential for wild-type function. The mutations were induced by either gamma-rays or ethyl methanesulfonate (EMS). All of the gamma-ray induced mutations were small or large chromosomal rearrangements, while all of the EMS mutations were G-->A transitions. These findings are consistent with the biochemical basis of the mode of action of each mutagen.