Point Mutations in the Stem Region and the Fourth AAA Domain of Cytoplasmic Dynein Heavy Chain Partially Suppress the Phenotype of NUDF/LIS1 Loss in Aspergillus nidulans

摘要

Cytoplasmic dynein performs multiple cellular tasks but its regulation remains unclear. The dyneinnheavy chain has a N-terminal stem that binds to other subunits and a C-terminal motor unit that containsnsix AAA (ATPase associated with cellular activities) domains and a microtubule-binding site locatednbetween AAA4 and AAA5. In Aspergillus nidulans, NUDF (a LIS1 homolog) functions in the dyneinnpathway, and two nudF6 partial suppressors were mapped to the nudA dynein heavy chain locus. Here wenidentified these two mutations. The nudAL1098F mutation resides in the stem region, and nudAR3086C isnin the end of AAA4. These mutations partially suppress the phenotype of nudF deletion but do notnsuppress the phenotype exhibited by mutants of dynein intermediate chain and Arp1. Surprisingly, thenstronger DnudF suppressor, nudAR3086C, causes an obvious decrease in the basal level of dynein’s ATPasenactivity and an increase in dynein’s distribution along microtubules. Thus, suppression of the DnudFnphenotype may result from mechanisms other than simply the enhancement of dynein’s ATPase activity.nThe fact that a mutation in the end of AAA4 negatively regulates dynein’s ATPase activity but partiallyncompensates for NUDF loss indicates the importance of the AAA4 domain in dynein regulation in vivo.