Monoclonal antibodies to type X collagen. Biosynthetic studies using an antibody to the amino-terminal domain

Monoclonal antibodies to chick type X collagen have been used to study the structure, biosynthesis, and location of type X in cartilage. The antibodies were produced by injecting purified type X collagen into female SJL/J mice and then fusing their spleen cells with Sp2/0 myeloma cells. Hybridoma culture supernatants were screened for antibodies to type X collagen by enzyme-linked immunosorbent assay and Western blots. Positive supernatants did not cross-react with other collagen types (I, II, IX, XI) or with fibronectin. Three monoclonal antibodies were chosen for further characterization. Two of them (1A6 and 6F6) recognize a pepsin-sensitive domain of type X collagen. Rotary shadowing showed that 1A6 and 6F6 both recognize the same end of type X, probably the aminoterminal non-triple helical domain. Amino acid sequencing of the intact protein and of the epitope-containing peptide confirmed that the antibody recognition sites for 1A6 and 6F6 are within the amino-terminal domain. Monoclonal antibody 2B3 reacts with the pepsinized (45 kDa) and weakly with the nonpepsinized (59 kDa) forms of type X collagen. The monoclonal antibodies were used for immunolocalization of type X in hypertrophic chondrocytes and reacted only with tissue samples from areas undergoing endochondral ossification, e.g. growth plate and fracture callus. Antibody 6F6, when coupled to Sepharose, selectively binds to type X collagen from cell and organ cultures. In a pulse-chase experiment, no processing of the 59-kDa form of type X could be detected. Two components with molecular masses of approximately 70 and 85 kDa, arising from a disulfide-bonded aggregate, were synthesized by both the permanent and calcifying cartilage organ cultures but did not react with the antibody, suggesting that these proteins are not related to type X. In summary, the pulse-chase results and the immune precipitation with monoclonal antibody 6F6 did not detect biosynthetic precursors larger than 59 kDa or proteolytically processed forms of type X.     

The thermal depolymerization of porcine submaxillary mucin

The time dependence of the molecular weight, radius of gyration, and hydrodynamic size distribution for porcine submaxillary mucin (PSM) in solution have been studied using static and dynamic light scattering. The weight average molecular weight (Mw) of PSM in 6 M guanidine HCl, pH 7, is initially 3 X 10(6) and decreases with time in three phases: rapidly from 3-2 X 10(6), less rapidly from 2-0.9 X 10(6), and slowly below 0.9 X 10(6). The rates of decrease are much greater at pH 2. The energy of activation associated with each phase is 20 kcal/mol, which is similar to that reported for peptide bond cleavage at an aspartic acid residue. Addition of mercaptoethanol to PSM in 6 M guanidine HCl leads to a rapid decrease in Mw to 0.9 X 10(6), followed by a very slow further decrease. These results suggest that native PSM consists of subunits (Mw = 0.9 X 10(6] that are linked by disulfide bonds to form dimers (Mw = 2 X 10(6] and then higher aggregates. This cross-linking appears to occur at unglycosylated regions of the protein core, which are believed to be richer in aspartic acid than the rest of the molecule.     

Thyroid hormones and the reactivities of genetic variants of human erythrocytic glucose-6-phosphate dehydrogenase

Thyroid hormones, throxine (T4) and triiodothyronine (T3) which are known to activate glucose-6-phosphate dehydrogenase (G6PD) activity in vivo act as substrate inhibitors of G6PD in vitro. T4 competitively inhibits NADP in human erythrocyte G6PD variants G6PDA, G6PDB and G6PDA- with inhibition constants of 2.40 +/- 0.90 X 10(-6), 3.44 +/- 0.63 X 10(-6) and 6.53 +/- 0.60 X 10(-6) mol/l, respectively. The inhibition is, however, noncompetitive with respect to G6P in the three variants. T3 also has similar inhibition pattern to T4 with inhibition constants for NADP of 1.9 +/- 0.08 X 10(-5) and 1.28 +/- 0.17 X 10(-5) mol/l for G6PDB and G6PDA-, respectively. cAMP on the other hand inhibits G6P competitively with inhibition constants 1.50 +/- 0.22 X 10(-4), 1.06 +/- 0.24 X 10(-4) and 1.76 +/- 0.14 X 10(-4) mol/l for G6PDB, G6PDA and G6PDA-, respectively. There are significant differences in the inhibition effects of T4 and cAMP with respect to NADP as substrates for the normal enzyme G6PDA or G6PDB and the deficient enzyme G6PDA- when NADP is the substrate, the latter being much more inhibited. The activation effect of thyroid hormones in vivo may therefore not be a direct result of thyroid hormone binding to the G6PD enzyme nor mediated through the action of cAMP but plausibly be through complexation of inhibitory trace metal ions by the thyroid hormones T4 and T3.     

ATP binding site mutagenesis reveals different subunit stoichiometry of functional P2X2/3 and P2X2/6 receptors

The aim of the present experiments was to clarify the subunit stoichiometry of P2X2/3 and P2X2/6 receptors, where the same subunit (P2X2) forms a receptor with two different partners (P2X3 or P2X6). For this purpose, four non-functional Ala mutants of the P2X2, P2X3, and P2X6 subunits were generated by replacing single, homologous amino acids particularly important for agonist binding. Co-expression of these mutants in HEK293 cells to yield the P2X2 WT/P2X3 mutant or P2X2 mutant/P2X3 WT receptors resulted in a selective blockade of agonist responses in the former combination only. In contrast, of the P2X2 WT/P2X6 mutant and P2X2 mutant/P2X6 WT receptors, only the latter combination failed to respond to agonists. The effects of α,β-methylene-ATP and 2-methylthio-ATP were determined by measuring transmembrane currents by the patch clamp technique and intracellular Ca(2+) transients by the Ca(2+)-imaging method. Protein labeling, purification, and PAGE confirmed the assembly and surface trafficking of the investigated WT and WT/mutant combinations in Xenopus laevis oocytes. In conclusion, both electrophysiological and biochemical investigations uniformly indicate that one subunit of P2X2 and two subunits of P2X3 form P2X2/3 heteromeric receptors, whereas two subunits of P2X2 and one subunit of P2X6 constitute P2X2/6 receptors. Further, it was shown that already two binding sites of the three possible ones are sufficient to allow these receptors to react with their agonists.     

Extrachromosomal deoxyribonucleic acid in wild-type and photosynthetically incompetent strains of Rhodopseudomonas spheroides.

Three covalently closed circular species of extrachromosomal deoxyribonucleic acid have been identified by electron microscopic analysis in strains of Rhodopseudomonas spheroides. The weights of these plasmids, as determined from contour length, are about 75 X 10(6), 66 X 10(6), and 28 X 10(6) daltons for both aerobically grown and photosynthetically grown R. spheroides strain 2.4.1 (NRS) and for the photosynthetically incompetent strain V-2 (obtained by N-methyl-N-nitro-N'nitrosoguanidine mutagenesis) and 74 X 10(6), 66 X 10(6) and 34 X 10(6) daltons for a second photosynthetically incompetent strain, SLS I (obtained by incubating strain 2.4.1 [NRS] in medium containing sodium lauryl sulfate). Buoyant densities uere found to be 1.717 g/cm3 (58% guanine plus cytosine) for the plasmids of 66 X 10(6), 28 X 10(6), and 34 X 10(6) daltons in weight and 1.724 g/cm3 (65% guanine plus cytosine) for those weighing about 75 X 10(6) daltons. Possible functions of these plasmids are discussed.     

Covalent carcinogenic O6-methylguanosine lesions in DNA. Structural studies of the O6 meG X A and O6meG X G interactions in dodecanucleotide duplexes

High-resolution proton and phosphorus nuclear magnetic resonance studies are reported on the self-complementary d(C1-G2-N3-G4-A5-A6-T7-T8-C9-O6meG10-C11-G12) duplexes (henceforth called O6meG X A 12-mer when N3 = A3 and O6meG X G 12-mer when N3 = G3), which contain symmetry-related A3 X O6meG10 and G3 X O6meG10 interactions in the interior of the helices. We observe inter-base-pair nuclear Overhauser effects (NOE) between the base protons at the N3 X O6meG10 modification site and protons of flanking G2 X C11 and G4 X C9 base-pairs, indicative of the stacking of N3 and O6meG10 bases in both O6meG X A 12-mer and O6meG X G 12-mer duplexes. We have assigned all the base and a majority of the sugar protons from two-dimensional proton-correlated and nuclear Overhauser effect experiments on the O6meG X A 12-mer duplex and O6meG X G 12-mer duplex in solution. The observed NOEs establish that the A3 and O6meG10 at the modification site and all other residues adopt the anti configuration about the glycosidic bond, and that the O6meG X A 12-mer forms a right-handed duplex. The interaction between the bulky purine A3 and O6meG10 residues in the anti orientation results in large proton chemical shift perturbations at the (G2-A3-G4) X (C9-O6meG10-C11) segments of the helix. By contrast, we demonstrate that the O6meG10 residue adopts a syn configuration, while all other bases adopt an anti configuration about the glycosidic bond in the right-handed O6meG X G 12-mer duplex. This results in altered NOE patterns between the base protons of O6meG10 and the base and sugar protons of flanking C9 and C11 residues in the O6meG X G 12-mer duplex. The phosphorus backbone is perturbed at the modification site in both duplexes, since the phosphorus resonances are dispersed over 2 parts per million in the O6meG X A 12-mer and over 1 part per million in the O6meG X G 12-mer compared to a 0.5 part per million dispersion for an unperturbed DNA helix. We propose tentative pairing schemes for the A3 X O6meG10 and G3 X O6meG10 interactions in the above dodecanucleotide duplexes.     

Coccidian parasites (Apicomplexa: Eimeriidae) from insectivores. IV. Four new species in Talpa europaea from England

Moles from England were examined for coccidian oocysts and all 64 Talpa europaea were infected; of 64 infected hosts, 56 (88%) had multiple infections representing two to six coccidian species when examined. Oocysts in 31 of the 64 samples remainedunsporulated. Three eimerians and one isosporan were studied from the 33 fecal samples that had sporulated oocysts and these are described as new species; Cyclospora talpae Pellérdy & Tanyi, 1968, and Isospora sofiae (Golemansky, 1978) Levine & Ivens, 1979, are redescribed; and Cyclospora sp., similar to C. talpae, is discussed. Sporulated oocysts of C. talpae are ellipsoidal, 14.3 X 9.6 (12-19 X 6-13) microns with sporocysts ovoid, 9.4 X 5.7 (6-13 X 4-8) microns; it was found in 21 of the 33 (63.6%) sporulated samples. Sporulated oocysts of Cyclospora sp. are subspheroidal to ellipsoidal, 12.5 X 8.9 (10-14 X 6-12) microns with sporocysts ovoid, 8.6 X 5.3 (6-10 X 4-6) microns; it was found in 21 of the 33 (63.6%) sporulated samples. Sporulated oocysts of Eimeria avonensis n. sp. are elongate-ellipsoidal, 15.0 X 9.6 (13-20 X 7-12) microns with sporocysts ovoid, 6.6 X 3.6 (5-9 X 3-7) microns; it was found in 15 of the 33 (45.5%) sporulated samples. Sporulated oocysts of Eimeria berea n. sp. are subspheroidal, 12.1 X 10.5 (10-15 X 8-14) microns with sporocysts ovoid, 6.3 X 3.9 (5-10 X 2-5) microns; it was found in 8 of the 33 (24.2%) sporulated samples.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epstein-Barr virus DNA. IX. Variation among viral DNAs from producer and nonproducer infected cells.

A comparative analysis of three Epstein-Barr virus DNAs from American patients with infectious mononucleosis (B95-8, Cherry, and Lamont) and four Epstein-Barr virus DNAs from African patients with Burkitt lymphoma (AG876, W91, Raji, and P3HR-1) indicated that the usual format of Epstein-Barr virus DNA includes a variable number of direct repeats of a 0.35 X 10(6)-dalton sequence (TR) at both ends of the DNA, a 9 X 10(6)-dalton sequence of largely unique DNA (Us), a variable number of repeats of a 2 X 10(6)-dalton sequence (IR), and a 89 X 10(6)-dalton sequence of largely unique DNA (UL). Within UL there was homology between DNA at 26 X 10(6) to 28 X 10(6) daltons and DNA at 93 X 10(6) to 95 X 10(6) daltons. The relative sequence order (TR, US, IR, UL, TR) did not vary among "standard" Epstein-Barr virus DNA molecules of each isolate. B95-8 DNA had an unusual deletion extending from 91 X 10(6) to 100 X 10(6) daltons, and P3HR-1 DNA had an unusual deletion extending from 23.5 X 10(6) to 26 X 10(6) daltons. There was sufficient variability among the EcoRI and BamHI fragments of the DNAs to identify each isolate specifically. However, we discerned no distinguishing features for the two geographic or pathogenic origins of the seven isolates. Three intracellular DNAs (Raji, Lamont, and Cherry) and one virion DNA (P3HR-1) were heterogenous in molecular organization and had subpopulations of rearranged or defective molecules. Some regions, particularly 59 X 10(6) to 63 X 10(6) daltons and sequences around TR, frequently participated in rearrangements. Restriction endonuclease maps of the standard and rearranged DNAs of the seven isolates are presented.     

Measurement of the susceptibility of paramagnetically labeled cells with paramagnetic solutions

A method of measuring the volumetric magnetic susceptibility, in which magnetically labeled cells or other particles are suspended in a paramagnetic solution of known susceptibility over the poles of a magnet, is presented. If the cells are more magnetic than the solution, they are attracted toward the poles; if they are less magnetic, they are repelled. If they have the same susceptibility as the solution, they do not move. Under this condition, the cells are said to be "isomagnetic" with the surrounding solution. Since the volumetric susceptibility of this solution is known, the susceptibility of the cells is obtained. Using the "isomagnetic" method, the volumetric susceptibilities of test metal powders were determined within +/- 8 X 10(-6) SI units. Yeast, colonic carcinoma, and liver cells, rendered magnetic with erbium chloride, had susceptibilities ranging from 13 to 20 X 10(-6). Particles of articular cartilage treated with erbium chloride were heterogeneous, with susceptibilities ranging between 50 and 125 X 10(-6), while particles of bone had a susceptibility of 560 to 580 X 10(-6). Eukaryotic cells labeled with ferritin attained susceptibilities of less than 1 X 10(-6).     

Polymeric structure of a high-molecular-weight glycoprotein from bovine cervical mucus.

A 16 X 10(6)-Mr glycoprotein isolated from bovine oestrus cervical mucus when reduced under conditions where disulphide-bond cleavage is essentially quantitative produces chains whose Mr from light-scattering and from sedimentation and diffusion data is some 4 X 10(6)-5 X 10(6). Pronase digestion of the chains indicates that glycosylated sequences of Mr 0.3 X 10(6)-0.5 X 10(6) are interspersed with enzyme-susceptible non-glycosylated peptide sequences.     

一株高毒力致病杆菌CB6的鉴定

从北京郊区果园采集的小卷蛾斯氏线虫（Steinernema carpocapsae）肠道内分离到一株具有较强杀虫和抑菌活性的致病杆菌菌株CB6。形态特征及生理生化特征测定结果表明,CB6菌株与致病杆菌属（Xenorhabdus）中的嗜线虫致病杆菌（X. nematophila）种的特征基本一致。测定了该菌株的16S rRNA序列并根据16S rRNA序列构建了系统发育树;在系统发育树中,CB6菌株与嗜线虫致病杆菌其他4个菌株形成一个类群,序列同源性大于99%。但CB6菌株的酪氨酸酶、脂酶（蛋黄）的产生、核糖产酸等生化特征与嗜线虫致病杆菌种内的其他菌株存在一定的差异,且具有更强的杀虫和抑菌活性。因此认为CB6菌株是嗜线虫致病杆菌的一个变种,命名为嗜线虫致病杆菌北京变种（X. nematophila var. pekingensis）。     

Characterization of two types of yeast ribosomal DNA genes.

The intragenic organization of ribosomal DNA from a diploid strain of Saccharomyces cerevisiae was analyzed by using recombinant DNA molecules constructed in vitro. Restriction analysis of the yeast ribosomal DNA with the EcoRI restriction enzyme indicated that eight restriction fragments were present in the ribosomal DNA of this strain: X' (1.87 X 10(6) daltons), A (1.77 X 10(6) daltons), B (1.48 X 10(6) daltons), C (1.22 X 10(6) daltons), D (0.39 X 10(6) daltons), E (0.36 X 10(6) daltons), F (0.22 X 10(6) daltons), and G (0.17 X 10(6) daltons). These fragments were distributed between two different types of ribosomal DNA genes, which had the restriction maps: (formula: see text) in which the underlined region shows the repeating unit. The diploid yeast strain contained approximately equal amounts of each of these two types of genes. The analysis of the recombinant DNA molecules also indicated that the yeast ribosomal genes are homogeneous and extensively clustered.     

Discovery of Streptococcus pneumoniae Serotype 6 Variants with Glycosyltransferases Synthesizing Two Differing Repeating Units

Streptococcus pneumoniae is a persistent, opportunistic commensal of the human nasopharynx and is the leading cause of community-acquired pneumonia. It expresses an anti-phagocytic capsular polysaccharide (PS). Genetic variation of the capsular PS synthesis (cps) locus is the molecular basis for structural and antigenic heterogeneity of capsule types (serotypes). Serogroup 6 has four known members (6A–6D) with distinct serologic properties, homologous cps loci, and structurally similar PSs. cps of serotypes 6A/6B have wciNα, encoding α-1,3-galactosyltransferase, whereas serotypes 6C/6D have wciNβ encoding α-1,3-glucosyltransferase. Two atypical serogroup 6 isolates (named 6X11 and 6X12) have been discovered recently in Germany. Flow cytometric studies using monoclonal antibodies show that 6X11 has serologic properties of 6B/6D, whereas 6X12 has 6A/6C. NMR studies of their capsular PSs revealed that 6X11 and 6X12 have two different repeating units with a distribution of ∼40:60 6B:6D and 75:25 6A:6C PS, respectively. Sequencing of the wciNα gene in 6X12 and 6X11 revealed single and double nucleotide substitutions, respectively, resulting in the amino acid changes A150T and D38N. Substitution of alanine with threonine at position 150 in a 6A strain was associated with hybrid serologic and chemical profiles like 6X12. The hybrid serotypes represented by 6X12 and 6X11 strains are now named serotypes 6F and 6G. Single amino acid changes in cps genes encoding glycosyltransferases can alter substrate specificities, permit biosynthesis of heterogeneous capsule repeating units, and result in new hybrid capsule types that may differ in their interaction with the immune system of the host.     

Macromolecular architecture and hydrodynamic properties of human cervical mucins

Cervical mucus glycoproteins (mucins) were extracted by using slow stirring in 6M-guanidinium chloride supplemented with proteinase inhibitors. Subsequent purification was achieved by isopycnic density-gradient centrifugation in CsCl/guanidinium chloride. The whole mucins (Mr 10 X 10(6) - 15 X 10(6)) were degraded into subunits (Mr 2 X 10(6) - 3 X 10(6)) by reduction. Trypsin digestion of subunits afforded glycopeptides (T-domains) with Mr 0.4 X 10(6). The relationship between the intrinsic viscosity and Mr for the whole mucins and the fragments suggests that cervical mucins are linear flexible macromolecules. This view is supported by hydrodynamic data.     

Evidence for a nonrandom base sequence in a Bacillus pumilus plasmid: EcoR1 endonuclease digestion of pPL576.

EcoR1 endonuclease digested the Bacillus pumilus plasmid pPL576 (molecular weight similar to 28 X 10-6) into three distinct size classes of linear fragments. The molecular weights of the fragments are 13.0 X 10-6, 0.5 X 10-6, and 6.5 X 10-6 by sucrose gradient analysis. By electron microscope analysis the three fragments account for about 99% of the intact plasmid. These results indicate that pPL576 molecules contain a nonrandom base sequence, and are consistent with the interpretation that pPL576 is autonomous and not the result of cyclization of random chromosome fragments.     

Localization of phosphatidylserine binding sites to structural domains of factor Xa.

Binding of short chain phosphatidylserine (C6PS) enhances the proteolytic activity of factor X(a) by 60-fold (Koppaka, V., Wang, J., Banerjee, M., and Lentz, B. R. (1996) Biochemistry 35, 7482-7491). In the present study, we locate three C6PS binding sites to different domains of factor X(a) using a combination of activity, circular dichroism, fluorescence, and equilibrium dialysis measurements on proteolytic and biosynthetic fragments of factor X(a). Our results demonstrate that the structural responses of human and bovine factor X(a) to C6PS binding are somewhat different. Despite this difference, data obtained with fragments from both human and bovine factor X(a) are consistent with a common hypothesis for the location of C6PS binding sites to different structural domains. First, the gamma-carboxyglutamic acid (Gla) domain binds C6PS only in the absence of Ca(2+) (k(d) approximately 1 mm), although this PS site does not influence the functional response of factor X(a). Second, a Ca(2+)-dependent binding site is in the epidermal growth factor domains (EGF(NC)) that are linked by Ca(2+) and C6PS binding to the Gla domain. This site appears to be the lipid regulatory site of factor X(a). Third, a Ca(2+)-requiring site seems to be in the EGF(C)-catalytic domain. This site appears not to be a lipid regulatory site but rather to share residues with the substrate recognition site. Finally, the full functional response to C6PS requires linkage of the Gla, EGF(NC), and catalytic domains in the presence of Ca(2+), meaning that PS regulation of factor X(a) involves linkage between widely separated parts of the protein.     

Molecular mechanisms of olfactory reception. VI. Kinetic characteristics of camphor interaction with binding sites of rat olfactory epithelium

Camphor binding to a possible receptor of rat olfactory epithelium has been studied within the ligand concentration range 10(-11)-10(-6) M. At these concentrations camphor is bound by a set of receptors. They are distinguished by both the affinity to the ligand (K1 = 5 X 10(-10) M, K2 = 3.5 X 10(-8) M, K3 approximately equal to 10(-6) M) and their amount in the epithelium. The differences in the affinities are due to different values of the association rate constant of camphor (k1), which varies from 10(6) M-1 X s-1 for the receptors with high affinity up to 2 X 10(2) M-1 X s-1 for those with low affinity. These data are discussed in terms of equilibrium and kinetic models of the receptor-stimulus interaction.     

Artificial insemination in the mouse with special reference to the effect of sperm numbers on the conception rate and litter size (author's transl)

Mature female mice (ICR-JCL), 8 to 12 weeks of age, were artificially inseminated at 8:30-9:30 a. m. on the day of estrus vaginal smear (about 3-7 hr after ovulation) with 3.18 X 10(6), 1.83 X 10(6) and 1.15 X 10(6) sperms from four, two and one cauda epididymidis, respectively, of adult males which were suspended in 50 microliter of a modified Krebs-Ringer-bicarbonate solution and incubated at 37 degrees C was under 5% CO2 in air for an hour. Immediately after insemination, pseudopregnancy induced by an artificial penis and a vaginal tampon. Out of 13 females inseminated with 3.18 X 10(6) sperms, 9 females showed placental signs and 8 of them gave birth to the mean 10.5+/-2.20 (M+/-S.D.) young at term. Four of 13 females having received 1.83 X 10(6) sperms became pregnant giving birth to the mean 4.3+/-2.1 (M+/-S.D.) young at term. On the other hand, 5 out of 6 females failed to become pregnant following insemination with 1.15 X 10(6) sperms, and only one showed a placental sign and gave birth to twelve young at term. It is concluded that the conception rate and litter size are both dependent on the number of sperms inseminated and that more than 3 X 10(6) sperms are necessary to get the conception rate and the litter size comparable to those in natural mating.     

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.

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.