Mlp2 (green) and spindle pole components (red) link during the cell cycle.

Mlp1 and Mlp2 proteins lie on the inner face of the budding yeast nuclear envelope, attached to nuclear pore complexes. On page 225, Niepel et al. demonstrate that Mlp2 protein is required for normal spindle pole body assembly and function.To learn what proteins interact with the Mlp duo, the team developed a rapid purification method that relies on disrupting cells while they are still frozen, preserving protein complexes and avoiding proteolysis.

As expected, Mlp1 and Mlp2 interact with one another. Also, Mlp2, but not Mlp1, bound to core components of the spindle pole body. Electron microscopy showed that Mlp2 interacts with mature spindle pole bodies, rather than with soluble precursors. Moreover, cells lacking Mlp2 had spindle pole bodies that were smaller than normal, formed aberrant spindle organizers within their nuclei, and frequently underwent incomplete cytokinesis.

The team hypothesizes that Mlp2 links nuclear pore complexes and spindle pole bodies, and that without this connection maintenance and duplication of spindle pole bodies is compromised. They imagine a network of Mlp1 and Mlp2 that supports the structure of the nuclear envelope, with Mlp2 facilitating the exchange and incorporation of components into the spindle pole body.