title: Physicochemical characterization of the ribosomal RNA species of the Mollusca. Molecular weight, integrity and secondary-structure features of the RNA of the large and small ribosomal subunits.
abstract: 1. The rRNA species of the Cephalopoda Octopus vulgaris and Loligo vulgaris were found to have unexpectedly high sedimentation coefficients and molecular weights. In 0.1 M-NaCl the L-rRNA (RNA from large ribosomal subunit) has the same s20 value as the L-rRNA of the mammals (30.7S), whereas the S-rRNA (RNA from small ribosomal subunit) sediments at a faster rate (20.1S) than the S-rRNA of both the mammals and the fungi (Neurospora crassa) (17.5S). The molecular weights of the L-rRNA were determined by gel electrophoresis in formamide and found to be 1.66 X 10(6) (Octupus) and 1.89 X 10(6) (Loligo); the mol.wt. of the S-rRNA of both species is 0.96 X 10(6), i.e. much larger than that of the mammals (0.65 X 10(6)) and almost coincident with that of the '23S' RNA of the prokaryotes. 2. By contrast, the less evolved Gastropoda and Lamellibranchiata (Murex trunculus and Macrocallista chione) have S-rRNA and L-rRNA species with mol.wts. of 0.65 X 10(6) and approx. 1.40 X 10(6).3. All the mature L-rRNA molecules of the cephalopoda are composed of two unequal fragments held together by regions of hydrogen-bonding having a similar, low, thermal stability in the two species; the molecular weights of the two fragments composing the L-rRNA are estimated to be 0.96 X 10(6) and 0.88 X 10(6) (Loligo) and 0.96 X 10(6) and 0.65 X 10(6) (Octupus). THe S-rRNA of both species is a continuous chain with exactly the same molecular weight (0.96 X 10(6)) as the heavier of the two fragments of the L-rRNA. 4. The secondary-structure features of the L-rRNA and S-rRNA species of the Caphalopoda were investigated by thermal 'melting' analysis in 4.0 M-guanidinium chloride; 60-70% of the residues are estimated to form short, independently 'melting' bihelical segments not more than 10 base-pairs in length. 5. Bases are unevenly distributed between non-helical and bihelical portions of the rRNA molecules, G and C residues being preferentially concentrated in bihelical comains. 6. The secondary-structure regions of the L-rRNA species of Octopus and Loligo are heterogenous, including two discrete fractions of independently 'melting' species that give rise to biphasic 'melting' profiles: a fraction consisting of shorter (G + C)-poorer segments (60-68% G + C, not more than 5 base-pairs in length) and a fraction consisting of longer (G + C)-richer segments (80-88% G + C, 5-10 base-pairs in length). No evidence for heterogeneity has been detected in the S-rRNa.
mesh_terms: D000818:Animals; D001482:Base Composition; D002501:Centrifugation, Zonal; D055598:Chemical Phenomena; D002621:Chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D008970:Molecular Weight; D008974:Mollusca / Q000032:analysis*; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D049831:Octopodiformes / Q000032:analysis; D012335:RNA, Ribosomal; D051381:Rats; D013045:Species Specificity
chemical_list: D012335:RNA, Ribosomal