title: Gene disruptions indicate an essential function for the LmmCRK1 cdc2-related kinase of Leishmania mexicana.
abstract: The generation of homozygous null mutants for the crk1 Cdc2-Related Kinase of Leishmania mexicana was attempted using targeted gene disruption. Promastigote mutants heterozygous for crk1 were readily isolated with a hyg-targeting fragment, but attempts to create null mutants by second-round transfections with a bie-targeting fragment yielded two classes of mutant, neither of which was null. First, the transfected fragment formed an episome; second, the cloned transfectants were found to contain wild-type crk1 alleles as well as hyg and ble integrations. DNA-content analysis revealed that these mutants were triploid or tetraploid. Plasticity in chromosome number following targeting has been proposed as a means by which Leishmania avoids deletion of essential genes. These data support this theory and implicate crk1 as an essential gene, validating CRK1 as a potential drug target. L mexicana transfected with a Trypanosoma brucel homologue, tbcrk1, was shown to be viable in an immcrk1 null background, thus showing complementation of function between these trypanosomatid genes. The expression of crk1 was further manipulated by engineering a six-histidine tag at the C-terminus of the kinase, allowing purification of the active complex by affinity selection on Nl(2+)-nitriloacetic acid (NTA) agarose.
authors.affiliation: Wellcome Unit of Molecular Parasitology, University of Glasgow, Anderson College, UK. j.mottram@udcf.gla.ac.uk
authors.forename: J C
authors.initials: JC
authors.lastname: Mottram
authors.forename: B P
authors.initials: BP
authors.lastname: McCready
authors.forename: K G
authors.initials: KG
authors.lastname: Brown
authors.forename: K M
authors.initials: KM
authors.lastname: Grant
mesh_terms: D000483:Alleles; D000818:Animals; D015152:Blotting, Northern; D015139:Blotting, Southern; D015153:Blotting, Western; D002364:Caseins / Q000378:metabolism; D002874:Chromosome Mapping; D016054:DNA, Protozoan / Q000032:analysis; D005786:Gene Expression Regulation; D005816:Genetic Complementation Test; D006639:Histidine / Q000235:genetics; D007894:Leishmania mexicana / Q000235:genetics*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009571:Nitrilotriacetic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D009942:Organometallic Compounds / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011003:Ploidies; D011494:Protein Kinases; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D016053:RNA, Protozoan / Q000235:genetics; D017384:Sequence Deletion; D014162:Transfection; D014346:Trypanosoma brucei brucei / Q000235:genetics
chemical_list: C077833:CRK protein, protozoan; D002364:Caseins; D016054:DNA, Protozoan; D009942:Organometallic Compounds; D015800:Protozoan Proteins; D016053:RNA, Protozoan; C088321:nickel nitrilotriacetic acid; D006639:Histidine; D011494:Protein Kinases; D009571:Nitrilotriacetic Acid