Identification and chromosomal location of tandemly repeated DNA sequencesin Allium cepa

A 314-bp tandemly repeated DNA sequence, named pAc074, was characterized in Allium cepa by fluorescence in situ hybridization (FISH) analyses using ra ndom amplified fragment as probe. The nucleotide sequences of the clone pAc 074 is partially homologous to the satellite DNA sequences, ACSAT1, ACSAT2, and ACSAT3, of A. cepa with 81%, 81% and 78% similarity, respectively. Our sequential C-banding and FISH with pAc074 probe also clearly showed a clos e relation between C-heterochromatin at telomeric region and pAc074 sequenc es on all the chromosomes except on chromosome 6. On the long arm of chromo some 7, pA074 sequences appeared as interstitial band which did not corresp ond to C-heterochromatin bands. Instead, the C-heterochromatin bands corres ponded with the 5S rDNA signals. This is the first evidence of simultaneous banding of the 5S rDNA and C-band in A. cepa.