Homologous Vs Ectopic Integration Oftransgene

In contrast to yeast, where the transforming DNA molecule commonly integrates at the related sequence by cross over (homologous recombination), integration in the filamentous fungi occurs commonly at unrelated sequences (heterologous or ectopic recombination). As an example, Figure 9.2 shows the partial restriction map of a circular plasmid carrying



Figure 9.2 (a) Map of plasmid used to obtain HygR transformants of Ascobolus immersus. Black thick lines correspond to hph genes, dotted lines are regions containing regulatory elements gpd promoter and trpC terminator from Aspergillus nidulans and restriction sites for Xbal (Xb), BamHl (B), EcoRI (E) and Seal (Sc), ampicilllin resistance (amp). (b) Southern hybridization analysis of transformants using a hph probe corresponding to a Sca1-Sca1 fragment. Transformants (lane 1 and 4) have integrated one copy of the transgene. Transformants (lane 2) and (lane 3) have integrated three and four copy of the transgene, respectively. Based on Rhounim et al. (1994).

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