Cla4p binds to Cdc28p. Cdc28p was enriched from whole-cell extracts of strains SY3409 and SY3357 (lanes 2 and 3, respectively) using p13SUC1-agarose beads or from extracts of SY3357 carrying pSF19 (CDC28-HA) (lane 4), SY3409 (lane 5), and SY3409 carrying pSF19 (lane 6), using HA antibody-conjugated agarose. Neither Cdc28p nor Cla4-MYC could be enriched from extracts using undecorated agarose beads (lane 1; SY3409). Top, Western (immunoprecipitation [IP]) analysis of Cla4-MYCp associated with Cdc28p-coated beads; middle, amount of Cla4-MYCp present in the whole-cell extract (WCE); bottom, amount of Cdc28p associated with the agarose beads.