A New Construct for Cloning DNA and Modeling the Structure of Drosophila melanogaster Polytene Chromosomes

Modification of P-element-based transformation vector pCaSpeR3 yielded a new construct, pICon, which contains the structural region of the Escherichia coli lacZ, the adjacent 5' and 3' regulatory regions of hsp70, pUC19, and two tandem FRTs. Owing to the hsp70 promoter, the pICon insertion site may be located on polytene chromosomes after heat shock by light or electron microscopy. The pUC19 sequence with a polylinker allows cloning of the genomic sequence adjacent to the 3' end of pICon by P-target rescue. Functional FRTs allow insertion or deletion of various DNA fragments. The construct is large (22,046 bp), forms easily detectable structures in polytene chromosomes, and may be used to study the structural and functional organization of the Drosophila melanogaster genome, in particular, to elucidate the causes of banding pattern formation. To map the molecular boundaries of interband 3C6/C7, the DNA sequence of this region was cloned between the two FRTs.