Chromosome arm length, and a species-specific determinant, define chromosome arm width [S. cerevisiae]

Mitotic chromosomes in different organisms adopt various dimensions. What defines chromosome dimensions is scarcely understood. Here, we compare budding and fission yeasts that harbor similarly sized genomes distributed amongst 16 or 3 chromosomes, respectively. Budding yeast chromosomes are thinner and characterized by shorter mitotic chromatin interactions. This remains the case even following chromosome fusions to form three fission-yeast-length entities, revealing a species-specific organizing principle that correlates with condensin binding site spacing. Unexpectedly, within each species, longer chromosome arms are always thicker, a trend also observed with human chromosomes. Arm length as a chromosome width determinant informs mitotic chromosome formation models. Overall design: 3 biological replicates of Hi-C in G1 phase and mitosis using budding yeasts with different chromosome numbers; two fusion strains of cerev (SY7 and SY12) that were from the BY4742 strain SY7 (8 chromosomes): 1+2, 3+4, 7+8, 9+10, 11, 13+12, 15 and 16+5+6+14 SY12 (3 chromosomes): 1+2+3+4+7+8+9+10, 13+12+15+11 and 16+5+6+14