Mutant/mutation
In the mutant the open reading frame of actin II is replaced by the ORF of actin I. The mutant thus contains two actin I genes, the endogenous gene under the contol of its own 5' and 3'UTRs and one under the control of the 5' and 3'UTRs of the actin II gene

Protein (function)
Actin, a cytoskeletal protein, has many diverse functions in eukaryotic cells ranging from roles in cell motility, cell division, vesicle trafficking to functions in cell signaling and regulation of transcription. A critical property of actin is its ability to form filamentous polymers (F-actin), and a plethora of proteins are involved in the highly dynamic regulation of F-actin formation . Actins are highly conserved proteins that often exist in multiple isoforms in the eukaryotic cell and their expression is regulated both spatially and temporally during development. The number of conventional actin genes varies among eukaryotic organisms. A few single cell eukaryotes, such as Saccharomyces cerevisiae, Toxoplasma gondii, and Trypanosoma brucei encode a single actin gene, which results in lethality when targeted with gene ablation approaches. Many organisms, however, have several conventional actin genes.Apicomplexan parasites all encode one major actin isoform, here termed Actin I. All apicomplexan parasites also contain a number of actin-related and actin-like proteins. Plasmodium species species stand out in that they all encode a second conventional actin, termed Actin II.

Phenotype analyses of mutants lacking the actin II gene (RMgm-632) indicate that Actin II plays a major role during the formation of the male gametes (no exflagellation of male gametocytes; no male gamete formation). Female gametes are fertile as shown in cross-fertilisation studies with fertile male gametes.

Phenotype
Phenotype analyses of mutants lacking the actin II gene (RMgm-632) indicate that Actin II plays a major role during the formation of the male gametes (no exflagellation of male gametocytes; no male gamete formation)

Phenotype analyses of the act2rep mutant show that this mutant can produce male gametes and ookinetes, indicating that that Actin I can partially restore the essential functions of Actin II during male exflagellation when its expression is controlled by the actin II regulatory elements.

Very low numbers of oocysts numbers are produced that fail to produce sporozoites. These observations indicate Actin II has two consecutive essential functions. In addition to the previously described role in male gametogenesis (RMgm-632), this actin isoform is also critical for sporogony.

Additional information
Evidence is presented that Actin II is expressed during ookinete development.

Other mutants
mutants lacking the actin II gene (RMgm-632)