Differential inhibition of sister chromatid condensation induced by 5-azadeoxycytidine in human chromosomes.

The deoxycytidine analogue 5-azadeoxycytidine (5-aza-dC) induces differential inhibition of sister chromatid condensation when cells are treated with this substance for two replication cycles, as the subsequent staining of metaphase chromosomes with Giemsa shows. The bifilarly substituted chromatid is dramatically longer than the unifilar one. A percentage of the metaphases treated with 5-aza-dC even show a complete undercondensation of the bifilarly substituted chromatid. The optimum conditions for inducing sister chromatid differentiation were determined. No method has been developed as yet to permit enhancement of the differential staining in 5-aza-dC-treated preparations. The interactions between 5-aza-dC and chromosomal DNA as well as the factors involved in the differential staining of sister chromatids are discussed.