sentence: Inhibition of its associated kinase activity by CKIs indicates that CYCA1 forms catalytically active complexes with A-type CDKs in maize endosperm , since CYCA1-associated CDK activity is strongly inhibited by maize KRP ; 1 and KRP ; 2 ( Coelho et al. 2005 ) , which belong to the ICK / KRP-type CKIs that typically bind to and inhibit complexes containing A-type CDKs ( reviewed by Wang et al. 2008 ) .