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Specificity of polyamine requirements for the replication and maintenance of different double-stranded RNA plasmids
Abstract:
We have shown previously that the M1 double-stranded (ds) RNA (i.e., the killer plasmid [KIL-k1]) that codes for a protein toxin requires spermidine or spermine for its replication. We now report that replication of two other ds RNA plasmids of yeast also requires polyamines: (i) M2 ds RNA [( KIL-k2]) and (ii) L-A-E, a ds RNA plasmid carrying the non-Mendelian genetic element [EXL]. Putrescine alone is sufficient to maintain L-A-E but is not sufficient to maintain either M1 ds RNA or M2 ds RNA, which require either spermidine or spermine. Once M1 or M2 or L-A-E is lost, it cannot be restored by the addition of polyamines. In contrast, L-A-HN, a ds RNA molecule that carries the cytoplasmic genes [HOK] and [NEX], is not lost during polyamine deprivation. It is striking that polyamine deprivation differentially affects L-A-E and L-A-HN, even though these two ds RNA molecules have more than 99% homology. L-C, which is the same size as L-A but very different in sequence, is also not lost on polyamine starvation.
Insights
Yeast double-stranded RNA (dsRNA) plasmids require specific polyamines for replication. Polyamines like spermidine and spermine are essential for M1 and M2 dsRNA maintenance, while L-A-E requires putrescine.
Area of Science:
- Molecular Biology
- Yeast Genetics
- RNA Biology
Background:
- Double-stranded RNA (dsRNA) plasmids are extrachromosomal genetic elements found in yeast.
- Replication of some dsRNA plasmids, like M1 (killer plasmid [KIL-k1]), is known to depend on polyamines such as spermidine or spermine.
- The specific polyamine requirements for other yeast dsRNA plasmids remain less understood.
Purpose of the Study:
- To investigate the polyamine requirements for the replication and maintenance of other yeast dsRNA plasmids, specifically M2 dsRNA ([KIL-k2]) and L-A-E ([EXL]).
- To compare the effects of polyamine deprivation on different dsRNA molecules, including those with high sequence homology.
Main Methods:
- Yeast cultures were subjected to polyamine deprivation.
- The presence and replication of specific dsRNA plasmids (M1, M2, L-A-E, L-A-HN, L-C) were monitored under different polyamine conditions (spermidine, spermine, putrescine).
- Sequence homology between different L-A dsRNA variants was analyzed.
Main Results:
- Replication of M2 dsRNA and L-A-E dsRNA also requires polyamines.
- Putrescine alone supports L-A-E maintenance, whereas M1 and M2 dsRNA require spermidine or spermine.
- Once lost, these dsRNA plasmids cannot be restored by polyamine addition.
- L-A-HN and L-C dsRNA molecules are not lost during polyamine deprivation, despite high homology between L-A-E and L-A-HN.
Conclusions:
- Yeast dsRNA plasmid replication is differentially regulated by specific polyamines.
- Polyamines are crucial for the maintenance of certain yeast dsRNA plasmids, with distinct requirements for different plasmid types.
- Sequence homology does not solely determine polyamine dependence, as evidenced by the differential behavior of L-A-E and L-A-HN.