Rapid generation of gene disruption constructs by in vitro transposition and identification of a Dictyostelium protein kinase that regulates its rate of growth and development

We describe a rapid method for creating Dictyo stelium gene disruption constructs, whereby the target gene is interrupted by a drug resistance cassette using in vitro transposition. A fragment of genomic DNA containing the gene to be disrupted is amplified by PCR, cloned into a plasmid vector using topoisomerase and then employed as the substrate in an in vitro Tn5 transposition reaction. The transposing species is a fragment of DNA containing a Dictyostelium blasticidin S resistance (bs^r) cassette linked to a bacterial tetracycline resistance (tet^r) cassette. After transposition the plasmid DNA is transformed into Escherichia coli and clones in which the bs^r-tet^r cassette is inserted into the Dictyostelium target DNA are identified. To demonstrate its utility we have employed the method to disrupt the gene encoding QkgA, a novel protein kinase identified from the Dictyostelium genome sequencing project. QkgA is structurally homologous to two previously identified Dictyostelium kinases, GbpC and pats1. Like them it contains a leucine-rich repeat domain, a small GTP-binding (ras) domain and a MEKK domain. Disruption of the qkgA gene causes a marked increase in growth rate and, during development, aggregation occurs relatively slowly to form abnormally large multicellular structures.