Kar1p

Kar1p is a spindle pole body (SPB) component in the budding yeast Saccharomyces cerevisiae. It localizes to the half-bridge region of the SPB and is required for duplication of the SPB during the cell cycle.

As a structural element of the SPB duplication machinery, Kar1p provides a scaffold that helps assemble a newly forming SPB adjacent to the existing one, coordinating with other core SPB components such as Cdc31p (centrin) and Sfi1p. This arrangement supports the proper assembly and function of both mother and daughter SPBs as cells progress through mitosis.

Genetic inactivation of KAR1 produces defects in SPB duplication, frequently resulting in monopolar spindles and mitotic arrest. These phenotypes underscore its essential role in ensuring correct spindle formation and chromosome segregation.

Kar1p is considered a conserved component of the SPB duplication pathway in fungi and has been studied to illuminate the mechanics of microtubule organization and spindle integrity in yeast. The KAR1 gene was identified in yeast genetic screens for spindle- and division-related phenotypes, and its product is described as a structural, non-enzymatic protein that remains associated with the SPB throughout the cell cycle.

In summary, Kar1p is a key structural protein of the yeast SPB duplication system, necessary for forming a functional spindle apparatus and maintaining mitotic fidelity. Its study contributes to a broader understanding of microtubule organization and centrosome-like structures in fungi.