Mutant/mutation
The mutant expresses the yeast Flp recombinase under the control of the promoter of uis4.
The mutant does not contain a selectable marker. This marker (the hdhfr gene) has been removed from the genome by using the Flp/FRT site-specific recombination (SSR) system (see below 'Protein-function'). Removal of the hdhfr gene has been achieved by  transmission of the mutant through mosquitoes, thereby activating expression of the Flp recombinase that resulted in the excision of the hdhfr gene which was flanked by FRT sequences.

Protein (function)
In the Flp/FRT site-specific recombination (SSR) system of yeast, the Flp recombinase recognizes the 34 bp FRT sites and excises any DNA located between two directly oriented sites (referred to as the FRTed sequence). The activity of Flp recombinase is  reduced at 37°C and above - temperatures in erythrocytic stages in the vertebrate host - and is maintained at 20°C –25°C, temperatures permissive for parasite development in the mosquito.

Phenotype
The phenotype analyses indicate that expression of Flp is specific for salivary gland sporozoites. Expression of Flp did not affect viability of infectivity of the different life cycle stages. By analysis of excision of the FRTed hdhfr selectable marker it was shown that Flp was only active in the sporozoite stages and that the Flp/FRT system in sporozoites was efficient in excision of FRTed DNA sequences from the genome.

Additional information
This mutant expressing Flp can be used for introducing additional DNA sequences (genes) that are flanked by FRT sequences. Subsequently these sequences can be removed by mosquito transmission. This 'conditional mutagenesis' approach allows for the analysis of the effect of removal of genes essential for blood stage development. For an example of using this approach see mutant RMgm-270

A derivative of the UIS4/Flp(−) mutant (RMgm-269)  that expresses bright GFP fluorescence via the constitutive HSP70 promoter is also available as a parasite “receiver” of conditional alleles of genes of interest. This mutant contains the pbdhfr selectable marker. Therefore, introduction of additional mutations is dependent on a second drug selectable marker (hdhfr).

See also mutant TRAP/FlpL(-) (RMgm-268) for a mutant expressing FlpL under the control of the trap promoter that is specifically switched on during oocyst development in midgut sporozoites.

Other mutants
RMgm-268: A mutant expressing FlpL under the control of the promoter of trap. It does not contain a drug-selectable marker.
RMgm-269: A mutant expressing Flp under the control of the uis4 promoter that is specifically switched on in sporozoites after salivary gland invasion. In addition it expresses GFP under the control of the constitutive hsp70 promoter. It contains the pbdhfr selectable marker.
RMgm-270: A 'conditional knock-out mutant of MSP-1', generated using the Flp/FRT system.