CDKs interact with c-Myb. (A) CDK6 and c-Myb are in a complex in human cells. Extracts from Jurkat T cells were prepared and analyzed for CDK6 expression using a total extract (lane 1) or samples that were first immunoprecipitated (IP) using anti-Myb antibodies (lane 2) or nonspecific antiserum (NS; lane 3). The samples were analyzed by Western blotting using anti-CDK6 antibodies for detection. The amount of sample analyzed in lane 1 is 10% of the amount used for the immunoprecipitations in lanes 2 and 3. (B) CDK coimmunoprecipitation. QT6 fibroblast cells were transfected with plasmids expressing c-Myb (lanes 1, 4-6, 9, 10), FLAG epitope-tagged CDK4 (lanes 2, 4, 7, 9), and FLAG epitope-tagged CDK6 (lanes 3, 5, 8, 10) as indicated at top. After 2 days, extracts were prepared and a small sample (10% of total) was saved for total extract analysis (lanes 1-5) while the remainder of each was subjected to immunoprecipitation using anti-FLAG beads (lanes 6-10). All the samples were analyzed by Western blotting using anti-Myb antibodies. The migration of the c-Myb protein is indicated at the right as is the immunoglobulin (IgG) band from the immunoprecipitation that cross-reacts with the second antibody used in the Western blot analysis.