The "8-kD" cytoplasmic dynein light chain is required for nuclear migration and for dynein heavy chain localization in Aspergillus nidulans

The heavy chain of cytoplasmic dynein is required for nuclear migration in Aspergillus nidulans and other fungi. Here we report on a new gene required for nuclear migration, nudG, which encodes a homologue of the "8-kD" cytop lasmic dynein light chain (CDLC). We demonstrate that the temperature sensi tive nudG8 mutation inhibits nuclear migration and growth at restrictive te mperature. This mutation also inhibits asexual and sexual sporulation, decr eases the intracellular concentration of the nudG CDLC protein and causes t he cytoplasmic dynein heavy chain to be absent from the mycelial tip, where it is normally located in wild-type mycelia. Coimmunoprecipitation experim ents with antibodies against the cytoplasmic dynein heavy chain (CDHC) and the nudG CDLC demonstrated that some fraction of the cytoplasmic dynein lig ht chain is in a protein complex with the CDHC. Sucrose gradient sedimentat ion analysis, however, showed that not all of the NUDG protein is complexed with the heavy chain. A double mutant carrying a cytoplasmic dynein heavy chain deletion plus a temperature-sensitive nudG mutation grew no more slow ly at restrictive temperature than a strain with only the CDHC deletion. Th is result demonstrates that the effect of the nudG mutation on nuclear migr ation and growth is mediated through an interaction with the CDHC rather th an with some other molecule (e.g., myosin-V) with which the 8-kD CDLC might theoretically interact.