Fig. 3. The CDK kinase activity of 35S::NtKIS1a lines is reduced. Protein extracts from wildtype (WT), two 35S::NtKIS1a Arabidopsis lines, one strong (S) and one medium (M), or buffer (C) were added to p9^CKSHs1 beads to purify CDK/cyclin complexes. Histone H1 phosphorylation (H1-P) was monitored and equal loading of histone H1 (H1) was controlled. Proteins bound to p9^CKSHs1 beads were recovered and immunoblotted with an antibody raised against the conserved CDK PSTAIR motif (PSTAIR). The histone H1 phosphorylation and the PSTAIR signals were quantified with NIH image 1.62 software. Their ratio was calculated and presented in the graph. The maximal value obtained in WT was referred as 100%.