IDENTIFICATION OF SHORT TANDEMLY REPEATED SEQUENCES IN EXTRACHROMOSOMAL CIRCULAR DNAS FROM DROSOPHILA-MELANOGASTER EMBRYOS

A sequence (scl) belonging to the recently identified dodeca satellite family was found to be a major family of extrachromosomal circular DN A molecules from Drosophila melanogaster embryos. The basic unit consi sts of the 11-bp repeat 5' ACTGGTCCCGT 3', is 63% G + C rich, and shar es some similarity with the Escherichia coli chi sequence. This family accounts for only about 0.06% of the genome but very likely for a hig her proportion of the circular DNA molecules. It is organized in the g enome into at least five main clusters contained in DNA fragments larg er than 20 kb and several minor clusters. These clusters are located i n the heterochromatic pericentromeric regions. Two other families of s imple repeated sequences, the 1.686 g/cm3 (5' AATAACATAG 3') and the 1 .705 g/cm3 (5' AAGAG 3') satellite DNAs, were also found in circular D NAs, while another family, the 1.672 g/cm3 (5' AATAT 3'), was not dete cted. The representation of the simple repeated sequences in circular molecules is not correlated to their genomic representation. Among the seven families of sequences identified to date in extrachromosomal ci rcular DNAs from embryos, the dodeca satellite, the 240-bp repeat of t he rDNA intergenic spacer, and the 1.688 and 1.705 g/cm3 Satellite DNA s are the most represented families, while the 5S genes, the histone g enes, and the 1.686 g/cm3 satellite DNA are present in a lower amount.