Isolation and characterization of the cDNA for an A-like cyclin in Adiantum capillus-veneris L.

We have isolated and characterized the cDNA for a homolog of a cyclin from the fern Adiantum capillus-veneris L. Three fragments of cDNAs for cyclin homologs were amplified by the PCR from the cDNA of germinating spores with degenerate primers that encoded the highly conserved region in the so-called cyclin box. We isolated a full-length cDNA for cyclin from a lambda ZAPII-cDNA library that has been derived from spores using an amplified fragment as a probe. The cDNA insert (Cyc-Ac1) in one positive clone was 2.0 kb in length, having an open reading frame of 1,599 bp that encoded 532 amino acids. The putative CycAc1 protein had a cyclin box and a destruction motif, and it was homologous to A-type cyclins. Northern blot analysis was performed to study the expression of CycAc1 during the first cell cycle in the haploid generation of the fern. CycAc1 mRNA was not detectable in dormant spores, during the first G1 phase, and at the onset of the S phase in imbibed spores after breaking of dormancy. This mRNA became detectable after the termination of the S phase, and it accumulated during the second G1 phase. Although CycAc1 was classified as an A-like cyclin, the failure to detect CycAc1 mRNA at the onset of the S phase suggests that CycAc1 might not play a role in the replication of DNA during the S phase.