AT-rich linkers in long range organisation of Drosophila DNA.

AT-rich segments were mapped in 6 different domains of the Drosophila melanogaster genome by partial denaturation of cloned genomic DNA segments and observation in the electron microscope (EM). As found in a previous investigation (Moreau et al., 1982), three types of AT-rich segments could be distinguished: 1) AT-rich linkers with a very high AT content, 600 +/- 200 bp long; 2) clusters of such AT-linkers extending over up to 10 Kbp and 3) AT-rich stretches which are shorter and of lower AT content compared to AT-linkers. Six genes previously localized in these domains were found to lie in relatively GC-rich segments framed by AT-rich elements of the 3 types: the Larval Serum Protein LSP-1 alpha gene is framed by 2 AT-linkers, the LSP-1 beta and LSP-2 genes by two AT-rich stretches, an the LSP-1 gamma gene by a cluster and a stretch. The 55 Kbp genomic segment encompassing the P6 gene contains and AT-cluster of about 15 Kbp and several AT-linkers and AT-rich stretches. The 85 Kbp domain containing the P1 gene includes 3 AT-rich clusters of about 10 Kbp each framing GC-rich domains punctuated by AT-linkers and stretches. This study shows that AT-mapping allows a rapid diagnosis of large genomic DNA domains in relation to the AT-rich segments which, possibly, are of significance with regard to genome organisation and function.