Fig. 3.

Both long and short PHC2 isoforms associate with CBX proteins. A, Schematic representation of the human PHC2 locus. Two transcripts are generated from the PHC2 locus by alternative transcriptional initiations. Exons are drawn by boxes. Gray boxes correspond to coding regions, whereas white boxes correspond to untranslated regions. B, Position of peptides identified by TAP-MS/MS on the PHC2 protein sequence. A peptide (underlined) matches to sequences specific to PHC2a long isoform and was identified specifically in a high molecular weight fraction of a TAP gel. Protein sequence of PHC2 is depicted. Part of the protein sequence corresponding to the PHC2b short isoform is in italic. The identified peptides are indicated as black boxes or underlined sequence on the PHC2 protein sequence. C, Co-immunoprecipitation analyses showing that CBX4 interacts with the PHC2a and PHC2b isoforms. HEK293 were transfected to express transiently FLAG-tagged CBX4 or CBX4[1–269] proteins together with and GFP-tagged PHC2a or PHC2b isoforms. Proteins were immunoprecipitated (IP) with an anti-FLAG antibody linked to agarose beads, separated by SDS-PAGE, and detected (WB) using the indicated αGFP or αFLAG antibodies. Levels of transfections were analyzed in total lysates.