The quantitative changes of a group of non-histone chromosomal proteins identified by its solubility, electrophoretic mobility and amino acid analysis as the high mobility group proteins HMG1 and HMG2, were studied throughout rooster spermatogenesis. The ratio HMG1/HMG2 remained constant (0.66 ± 0.04) during the transition from dividing meiotic and premeiotic cells to nondividing spermatids and from transcriptionally active cells (spermatogonia, spermatocytes and early spermatids) to transcriptionally inactive late spermatids. The ratio HMG1/nucleosomal histone and HMG2/nucleosomal histone increase markedly at the end of spermiogenesis during the transition from nucleohistone to nucleoprotamine when nucleosomes are being disassembled. The high mobility group chromosomal proteins HMG1 and HMG2 were not detectable in the nuclei of rooster spermatozoa.
