Studies on Nucleic Acids of Living Fossils

Elution profiles on gel filtration (Sephadex G-100) and sedimentation profiles on sucrose density gradient were compared for transfer RNAs (tRNAs) from two “living fossils“ and from eleven species of “present organisms.” These various species of tRNAs showed a similar coefficient of distribution, Kd value, in the denatured state, which reflects a similar molecular length on an average. However, they were classified into two groups from their Kd values in the native state. Group I (Kd=0.17) includes five bacterial tRNAs (E. coli, S. typhimurium, B. subtilis, B. cereus and P. vulgaris) and yeast tRNA. Group II (Kd≥0.19) includes five species of tRNAs from fungus (A. oryzae), plant (spinach), insect (silkworm) and mammalian (rat liver and rabbit liver). tRNAs from living fossils (brachiopod Lingula and horseshoe crab Limulus) are also included in the group II, although their Kd values are somewhat larger. Sedimentation profiles on sucrose density gradient supported this classification.