We have previously reported that only a single Cdk1-related G1 and G1/S cyclin homologue was found in the genome sequence of the pathogenic basidiomycetous yeast Cryptococcus neoformans (C neoformans) and designated it CnCln1. Surprisingly, CnCln1 was not only able to complement the function of the Cl cyclins of the ascomycetous budding yeast Saccharomyces cerevisiae (S. cerevisiae), such as ScCln3, but also the G1/S cyclins of S. cerevisiae, such as ScCln1 and ScCln2. In this study, we investigated how CnCln1 cooperates with the cyclin-dependent kinases of S. cerevisiae (ScCdk1) and substitutes the function of Cl and G1/S cyclins of S. cerevisia from a point of view of their structure-function relationship. Our in silica analysis demonstrated that the CnCln1/ScCdk1 complex was more stable than any of the yeast cyclin and ScCdk1 complexes. Thus, these results are consistent with in vitro analysis that has revealed the flexible functional capacity of CnCln1 as a Cdk1-related G1 and G1/S cyclins of S. cerevisiae. (C) 2011 Elsevier Inc. All rights reserved.