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The ATF-1 gene encodes for a transcription factor normally regulated by cAMP (Hai et al. 1989, Yoshimura et al. 1990). Recently, it has been shown to be involved in the recurrent t(12;22) translocation observed in soft tissue malignant melanoma, in a fusion gene with the EWS gene (Zucman et al. 1993). We report here on its precise localization on chromosome 12 by fluorescence in situ hybridization.

In a series of ten patients affected by DiGeorge syndrome, we screened, by high resolution banding and fluorescent in situ hybridization of a cosmid probe, for microdeletions associated with this syndrome. In the ten patients, a microdeletion was demonstrated by in situ hybridization, but suspected only in two patients by high resolution banding.

Polymerase chain reaction amplified products promoted by oligonucleotides complementary to the highly repetitive human Alu sequence can be used for in situ hybridization on metaphase chromosomes to investigate the human content of a hybrid cell line. The TC65 primer, which combines the advantages of promoting the amplification of large inter-Alu sequences together with only small flanking Alu sequences, enables a simple and precise characterization to be made, with a high signal to noise ratio. Total human DNA is an efficient competitor in the removal of non-specific signals. The use of this oligonucleotide should be considered in the characterization of the human content of hybrids or in the generation of specific reagents for chromosome decoration.