A 37-kb fragment common to the pericentromeric region of human chromosomes 13 and 21 and to the ancestral inactive centromere of chromosome 2.

A YAC clone from a chromosome 21-specific partial library was localized by in situ hybridization to the pericentromeric region of chromosomes 13 and 21 and to the long arm of chromosome 2, where an ancestral inactive centromere is present. Restriction mapping of the insert showed that it may contain tandemly repeated DNA. Probes for alpha-satellite and satellite II and III failed to hybridize with the cloned DNA. Shotgun subcloning might reveal a sequence that seems to be specific for chromosome 21. Alu-PCR was performed to generate probes from the YAC clone to map it more precisely, using a somatic hybrid containing only human chromosome 21. The inter-Alu sequences thus isolated were found to be clustered in an approximately 37-kb-long fragment common to chromosome 2, 13, and 21, which might be involved in the centromeric function of these chromosomes.