Mutant/mutation
The mutant expresses a C-terminal GFP-tagged version of CYC3

Protein (function)
Plasmodium species encode only three identifiable cyclins–CYC1, CYC3 and CYC4. A P. falciparum gene (encoded by PF3D7_1227500) annotated as PfCYC2 did not show a significant match to any of the cyclin-specific HMMs built during these analyses (even at extremely liberal thresholds), nor to the domains built by PFam. This protein was originally identified as a cyclin on the basis of a very limited similarity to a cyclin A from the sea star Patiria (Asterina) pectinifera (13% identity across alignable length), but it lacks key alignable residues across most of the cyclin box and has no detectable cyclin-like function in biochemical assays. These data strongly suggest that CYC2 is not a true cyclin.

The Plasmodium cyclin repertoire is highly unusual in that it entirely lacks Group I, the largest group of cyclins. This group contains most canonical cyclin families that regulate specific cell cycle transitions with their CDK partners: Cyclin D-CDK4/6 for G1 progression, Cyclin E-CDK2 for the G1/S transition, Cyclin A-CDK2 for S phase progression and CyclinA/B-CDK1 for mitosis, although in fission yeast, all cell cycle transitions are driven by a single Cyclin B/CDK complex (CDC13/CDC2). In keeping with this key role and previous analyses, Group I cyclins were found in all non-apicomplexan species examined, including the alveolate Tetrahymena thermophila. However, none of the apicomplexan species examined contained Group I cyclins, except Cryptosporidium, which was found to encode three Group I cyclins of indeterminate family, suggesting that there has been a loss of Group I cyclins during the evolution of apicomplexan lineages. Plasmodium species encode only one cyclin, CYC3, from the P family (Group II) and two Group III cyclins from families H and L. The cyclin P family is not found in animals, but includes many plant cyclins and Pho80 in budding yeast, which link nutritional sensing to cell cycle progression. In contrast, both H and L families are associated with transcription: the CDK7/Cyclin H/MAT1 complex functions as a Cdk-activating kinase in cell cycle regulation and as a modulator of the general transcription factor TFIIH. Similarly, CDK11-Cyclin L complex in fission yeast regulates the formation of the Mediator complex, a coactivator of RNA polymerase II transcription. 

Phenotype
Analyses of mutant lacking CYC3 (RMgm-1355, RMgm-1301) showed reduced oocyst and sporozoite formation. Aberrant oocyst formation

CYC3-GFP parasites were able to complete the full life cycle with no detectable phenotype observed from tagging with GFP including oocyst development at 14 days post infection (dpi) in mosquitoes. Live imaging of parasites revealed CYC3-GFP presence throughout the parasite cell body with a predominantly cytosolic localisation at most of the key Plasmodium life cycle stages examined (trophozoite, male and female gametocyte, zygote, ookinete, oocyst and salivary gland sporozoite). Deconvolution fluorescence imaging showed that CYC3-GFP was uniformly present throughout both the cytoplasm and the nucleus in trophozoites, gametocytes and ookinetes and noticeably enriched in the nucleus of ookinetes.
Fluorescent imaging showed no detectable CYC3-GFP expression in oocysts at 5 and 7 dpi. Expression of CYC3-GFP was first observed at low levels in the majority of oocysts at 10 dpi with the highest expression detected at 14 dpi. Oocysts that had formed fully mature sporozoites showed the highest protein expression. After 14 dpi, a decrease was observed in CYC3-GFP expression in oocysts up to day 21pi.

Additional information
Quantitative RT-PCR (qRT-PCR) was used to investigate the RNA levels of cyc1, 3 and 4 in six stages of the wild-type parasite life cycle. The transcription profiles showed expression of the cyclins throughout parasite development with the highest RNA levels for all three cyclins found in gametocytes (both non-activated and activated) and schizonts (particularly cyc4). The cyc3 RNA level was highest in non-activated gametocytes, whereas for cyc1 and cyc4, the levels were highest in activated gametocytes.

Other mutants
See RMgm-1356 for a mutant expressing a C-terminal GFP-tagged version of CYC3
See RMgm-1301 for an independent mutant lacking expression of CYC3