Abstract

Our group has reported the unique cell cycle pattern of Cryptococcus neoformans, different from that of the model budding yeast Saccharomyces cerevisiae. To clarify the cell cycle mechanisms, homologues of cell cycle control genes in C. neoformans were cloned. We have previously reported the cloning of the CDC28/Cdc2 homologue, CnCdk1 and three Cdk1 cyclin homologues: two B-type G2/M cyclins and a single G1 cyclin, CnCln1. Further search of the C. neoformans genome database however did not yield additional ORFs with G1 cyclin similarities. Sequence analysis and comparison with other cyclin sequences showed that CnCln1 possesses the typical amino acid residues conserved among G1 cyclins. Complementation test in a triple G1 cyclin mutant showed that CnCln1 can perform G1 functions in S. cerevisiae. We also attempted and succeeded, in obtaining a deletion mutant of CnCln1 by biolistic transformation. G1 cyclin deletion in C. neoformans resulted to abnormally enlarged cells, delayed growth and subsequent hyphal formation, indicating a role for CnCln1 in morphogenesis; but apparently is not essential, pointing out to the existence of bypass mechanisms to replace its functions.