CALCIUM MODULATION OF POLYAMINE TRANSPORT IS LOST IN A PUTRESCINE-SENSITIVE MUTANT OF NEUROSPORA-CRASSA

Putrescine transport in Neurospora is saturable and concentrative in dilute buffers, but in the growth medium putrescine simply equilibrates across the cell membrane. We describe a mutant, puu-1, that can concentrate putrescine from the growth medium because the polyamine transport system has lost its normal sensitivity to Ca2+. The wild type closely resembles the mutant if it is washed with citrate and ethylene glycol bis(β-aminoethyl ether)N,N′-tetraacetic acid. The mutant phenotype also appears in the wild type after treatment with cycloheximide. The results suggest that putrescine uptake is normally regulated by an unstable Ca2+ -binding protein that restricts polyamine uptake. This protein is evidently distinct from the polyamine-binding function for uptake, which is normal in mutant and in cycloheximide-treated wild type cells. The puu-1 mutation, stripping of Ca2+, and cycloheximide treatment all cause an impairment of amino acid transport, indicating that other membrane transport functions rely upon the product of the puu-1+ gene. Preliminary evidence suggests that the putrescine carrier is not the Ca2+-sensitive, low-affinity K+-transport system, but K+ efflux does accompany putrescine uptake. © 1991.