Using site-directed mutants of ARL1 predicted to alter nucleotide binding, we examined phenotypes associated with the loss of ARL1 , including effects on membrane traffic and K (+) homeostasis. The GTP-restricted allele, ARL[Q72L] , complemented the membrane traffic phenotype (CPY secretion), but not the K (+) homeostasis phenotypes (sensitivity to hygromycin B, steady-state levels of K (+) , and accumulation of (86) Rb (+) ), while the XTP-restricted mutant, ARL1[D130N] , complemented the ion phenotypes, but not the membrane traffic phenotype. A GDP-restricted allele, ARL1[T32N] , did not effectively complement either phenotype.
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