Approximately 5 million cells from each cell line were cross-linked with 1% formaldehyde for 15 min and excess formaldehyde quenched by addition of glycine (0.625 M). Nuclei were prepared and collected for sonication in 1% SDS-buffer DNA was enrepaired, followed by "A" attachment, adapter ligation and 15 cycles of PCR with multiplex primers. Size selection was performed with 1.5% low melting agarose gels.