Because Kar5p localizes near the SPB, and because the SPB-enriching factor is also present in mitotic cells, we suspected that Kar5p is anchored by an SPB half-bridge protein.
This suggests that Bbp1 and possibly other pore membrane components of the SPB may localize to early SPB duplication structures.
In particular, because Mps1 is required for SPB duplication [20], the new SPB might be partly defective even after this requirement is bypassed with cdc34-2.
Our observation that proteins involved in membrane insertion, such as Mps2, Bbp1, and Ndc1, also accumulate at the new SPB early in duplication suggests that SPB assembly and NE insertion are coupled events during SPB formation in wild-type cells.
We observed that Kar5-TM3-GFP still enriched at the SPB in mitotic cells, demonstrating that the SPB-enriching factor is not restricted to pheromone treated cells.
Examination of a GFP-tagged SPB component, Sid4 [ 43], clearly revealed two SPB signals in cells containing monopolar spindles, indicating that the SPBs had duplicated.
These data make Mlp2 a likely SPB remodeling factor and implicate nuclear pore proteins in SPB assembly and remodeling.
Note the two lamellar structures (a duplicated SPB) and that the microtubules are gathering at the SPB from different directions.
Among them, five common rootstocks in Spain were shown to be fertile in semi-natural conditions (5BB Kober: 24.4 seeds per bunch (SPB), 161-49 Couderc: 76.6 SPB, 19-62: 17.9 SPB, 41B MGT: 18.7 SPB and 1202C: 28.8 SPB [25]).
In these cases, the MT end lacking a SPB causes tether formation upon elongation but the opposite SPB-containing end shows normal nuclear curvature.
Kar5p is a highly conserved transmembrane protein that localizes adjacent to the spindle pole body (SPB), mediates nuclear envelope fusion, and recruits Prm3p adjacent to the SPB.
