Abstract
The polyamines putrescine, spermidine, and spermine are required for normal eukaryotic cellular functions. However, the minimum requirement for polyamines varies widely, ranging from very high concentrations (mm) in mammalian cells to extremely low in the yeast Saccharomyces cerevisiae Yeast strains deficient in polyamine biosynthesis (spe1Δ, lacking ornithine decarboxylase, and spe2Δ, lacking SAM decarboxylase) require externally supplied polyamines, but supplementation with as little as 10-8 m spermidine restores their growth. Here, we report that culturing a spe1Δ mutant or a spe2Δ mutant in a standard polyamine-free minimal medium (SDC) leads to marked increases in cellular Mg2+ content. To determine which yeast Mg2+ transporter mediated this increase, we generated mutant strains with a deletion of SPE1 or SPE2 combined with a deletion of one of the three Mg2+ transporter genes, ALR1, ALR2, and MNR2, known to maintain cytosolic Mg2+ concentration. Neither Alr2 nor Mnr2 was required for increased Mg2+ accumulation, as all four double mutants (spe1Δ alr2Δ, spe2Δ alr2Δ, spe1Δ mnr2Δ, and spe2Δ mnr2Δ) exhibited significant Mg2+ accumulation upon polyamine depletion. In contrast, a spe2Δ alr1Δ double mutant cultured in SDC exhibited little increase in Mg2+ content and displayed severe growth defects compared with single mutants alr1Δ and spe2Δ under polyamine-deficient conditions. These findings indicate that Alr1 is required for the up-regulation of the Mg2+ content in polyamine-depleted cells and suggest that elevated Mg2+ can support growth of polyamine-deficient S. cerevisiae mutants. Up-regulation of cellular polyamine content in a Mg2+-deficient alr1Δ mutant provided further evidence for a cross-talk between Mg2+ and polyamine metabolism.
Highlights
The polyamines putrescine, spermidine, and spermine are required for normal eukaryotic cellular functions
These findings indicate that Alr1 is required for the up-regulation of the Mg2؉ content in polyamine-depleted cells and suggest that elevated Mg2؉ can support growth of polyamine-deficient S. cerevisiae mutants
A high level of cellular polyamines is required for mammalian cell proliferation, and polyamine homeostasis is tightly regulated by intricate mechanisms [6]
Summary
In a yeast spe2⌬ mutant cultured in a medium containing Ͻ10Ϫ8 M spermidine, spermidine became severely limiting, and as much as ϳ50% of the total cellular spermidine was mobilized for hypusine synthesis These findings suggest that hypusination of eIF5A is the most critical function of polyamines in yeast, and that, unlike mammalian cells, yeast do not require a high intracellular concentration of polyamines for growth. Examination of double mutant strains lacking one polyamine biosynthesis gene (SPE1 or SPE2) and one Mg2ϩ transporter gene (ALR1, ALR2, or MNR2) indicated that Alr alone was required for this elevated Mg2ϩ accumulation Consistent with this observation, Alr was found to be essential for the survival and growth of polyamine-deficient spe1⌬ and spe2⌬ cells. The elevation of the cellular polyamine levels in the Mg2ϩ-deficient alr1⌬ mutant cultured in YPD2 further suggests an interaction between polyamine and Mg2ϩ metabolism
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
