Direct evidence for homologous sequences on the paracentric regions of human chromosome 1.

Calcyclin is a member of the S100 family of proteins, many of which are encoded by genes that have been localized to the proximal long arm of human chromosome 1 (bands q21-q22). A 450-kb yeast artificial chromosome clone containing the human calcyclin gene was identified by PCR screening and used as a probe for fluorescence in situ hybridization (FISH). Along with the expected hybridization to 1q21, simultaneous, specific hybridization to the centromeric region of the short arm of chromosome 1 was also observed. An identical pattern of hybridization was observed when microdissected 1q21 DNA sequences were used as a probe for FISH, confirming the presence of homologous sequences flanking both sides of the centromere of human chromosome 1. These results are consistent with a model in which human chromosome 1 arose by insertion of the centromere and heterochromatin into an ancestral chromosome containing chromosome-specific repetitive sequences.