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(beta-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 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 Ca(2+)-sensitive, low-affinity K(+)-transport system, but K+ efflux does accompany putrescine uptake.
Davis
R H
RH
Department of Molecular Biology and Biochemistry, University of California, Irvine 92717.
Ristow
J L
JL
Howard
A D
AD
Barnett
G R
GR
D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D002951:Citrates / Q000494:pharmacology; D019343:Citric Acid; D003513:Cycloheximide / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D009154:Mutation; D009492:Neurospora crassa / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011073:Polyamines / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011700:Putrescine / Q000378:metabolism / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013095:Spermidine / Q000378:metabolism / Q000494:pharmacology
D002951:Citrates; D011073:Polyamines; D019343:Citric Acid; D004533:Egtazic Acid; D003513:Cycloheximide; D012964:Sodium; D011188:Potassium; D002118:Calcium; D013095:Spermidine; D011700:Putrescine