Numerous histone H3 variants are differentially expressed in the course of macronuclear differentiation in Stylonychia lemnae. A. Conservation of sequence motifs adjacent to N-terminal lysine residues and chaperone recognition sites in human H3.1 (top line) and Stylonychia histone H3 variants. The descending order of Stylonychia H3 variants reflects the phylogenetic distance compared to human H3.1. B. Agarose gel electrophoresis of PCR products amplified from developmental stage-specific cDNA. C. Quantitative Real Time PCR analysis of Stylonychia H3 variants expression. The morphology of developing macronuclei - revealed by confocal laser scanning microscopy of To-Pro-3 stained DNA - at successive stages is shown in relation to the time scale (hours post conjugation).