Abstract

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 Ca 2+. 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 Ca 2+ -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 Ca 2+, 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 Ca 2+-sensitive, low-affinity K +-transport system, but K + efflux does accompany putrescine uptake.

Highlights

  • Puu-1, that can concentrate putrescine from the growth medium because the polyamine transport system has lost its normal sensitivity to Ca2+

  • The results suggest that putrescine uptake is normally regulated by an unstable Ca2+-binding protein that restricts polyamine uptake

  • This protein is distinct from the polyamine-binding function for uptake, which is normal in mutant and in cycloheximide-treated wild type cells

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Summary

Introduction

Putrescine transport in Neurospora is saturable and concentrative in dilute buffers, but in the growth medium putrescine equilibrates across the cell membrane. Puu-1, that can concentrate putrescine from the growth medium because the polyamine transport system has lost its normal sensitivity to Ca2+. The mutant phenotype 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 distinct from the polyamine-binding function for uptake, which is normal in mutant and in cycloheximide-treated wild type cells. Preliminary evidence suggests that the putrescine carrier is not the Ca’+-sensitive, low-affinity K+-transport system, but K+ efflux does accompany putrescine uptake

Methods
Results
Conclusion

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