Northern blot analysis showing the expression of selected members of the Pc-G family in human and murine hematopoietic cell lines. Five micrograms of total RNA isolated from each cell line was hybridized to probes specific to HP1^Hsα (14 hours of exposure), HP1^Hsγ (5.5 hours),M31 (96 hours), M32 (6 days), BMI-1 (14 hours), and 18S rRNA (4 minutes).