Translocation ofNeurospora crassaTranscription Factor NUC-1 into the Nucleus Is Induced by Phosphorus Limitation

Abstract

Peleg, Y., Addison, R., Aramayo, R., and Metzenberg, R. L. 1996. Translocation ofNeurospora crassatranscription factor NUC-1 into the nucleus is induced by phosphorus limitation.Fungal Genetics and Biology20,185–191. NUC-1, a basic helix–loop–helix zipper protein, activates the expression of several genes involved in phosphorus acquisition inNeurospora crassa.In the present study we investigated whether posttranscriptional mechanisms control the activity of NUC-1. The NUC-1 level was higher (up to fivefold) in wild-type cells grown at low external phosphate concentration and in mutant strains expressing the phosphorus acquisition genes constitutively than in a wild-type strain grown at high external phosphate concentration. Using indirect immunofluorescence we demonstrated that NUC-1 is localized at least predominantly in the cytosol when wild-typeN. crassais grown with an adequate supply of phosphate, whereas NUC-1 is largely concentrated in the nucleus upon limitation of external phosphate. In mutant strains expressing the phosphorus acquisition genes constitutively, NUC-1 localization was also primarily in the nucleus. Thus, subcellular compartmentation of regulatory proteins is an important mechanism in regulating gene expression in filamentous fungi.