Mutant/mutation
In the promoter swap' mutant: the promoter of the endogenous apc3 gene is replaced by the promoter of ama1 (PBANKA_0915000). In addition the mutant expresses GFP under the constitutive eef1a promoter.

Protein (function)
One essential component that drives the cell cycle, and particularly mitosis, in many eukaryotic systems is the Anaphase Promoting Complex/Cyclosome (APC/C). The APC/C is a multi-subunit E3 ubiquitin ligase that promotes cell-cycle progression by covalently tagging regulators such as securin and cyclin B1 with ubiquitin leading to their proteolysis by the proteasome. The mammalian APC/C has 14 core components, and several key adaptor subunits, including cell division cycle protein 20 (CDC20) and the related CDH1. Intriguingly, only four APC/C components have been identified as coded by the Plasmodium genome: APC10, APC11 and APC3 (a tetratricopeptide repeat [TPR] containing subunit), along with CDC20.
During the Plasmodium life cycle, there are two atypical mitotic processes: one that resembles endomitosis occurs during asexual multiplication, for example, during blood stage schizogony, and another that occurs during the sexual stage - the formation of microgametes (male progenitor sex cells) in the mosquito midgut. During schizogony, genome duplication and segregation proceed via the formation of an intra-nuclear spindle without disintegration of the nuclear membrane, resulting in a multinucleated syncytium called a schizont. In microgametogenesis, exposure of the male gametocyte to mosquito midgut factors results in ‘activation’ of the microgametocyte, which undergoes three rounds of rapid genome duplication from haploid to octaploid, followed by simultaneous chromatin condensation and nuclear budding. Each condensed haploid nucleus and associated MTOC, together with a basal body, axoneme and flagellum, is incorporated into the microgamete, which egresses from the main cellular body in a process termed exflagellation.

Phenotype
APC3 is essential for blood stage development/multiplication (see RMgm-4430 for unsuccessful attempts to disrupt the apc3 gene). In the 'promoter-swap' mutant the promoter of apc3 is replaced by an 'asexual blood stage’ promoter that is silent (or has a strongly reduced activity) in gametocytes (the promoter of ama1, PBANKA_0915000).

The mutant shows the following phenotype: Normal blood stage development/multiplication. No male gamete formation: in vitro activation of microgametocytes did not result in microgametogenesis as microgamete formation and exflagellation were not observed. Normal DNA replication in activated male gametocytes (up to the octoploid value). Normal axoneme formation. Female gametes are fertile (as shown in crossing-experiments).

Additional information
Evidence is presented that that APC3 is associated with the MTOC-like centriolar plaque during schizogony and male gametogenesis, but is not associated with the other APC/C components. However, it is required for chromosome condensation and cytokinesis, but not DNA replication, during microgamete formation.

Other mutants
see RMgm-4430 for unsuccessful attempts to disrupt the apc3 gene