Mutants with altered muscle structure in Caenorhabditis elegans

In the small nematode, Caenorhabditis elegans, mutants with a disorganized myofilament lattice structure have been identified by polarized light and electron microscopy. Genetic analysis places the mutations in 12 complementation groups which are distributed over the six linkage groups of C. elegans. The phenotypes are described for the mutants from the 9 complementation groups not previously reported on in detail. Most are paralyzed, but some exhibit essentially normal movement; mutants of two loci show changes only in later larval stages and adulthood. Morphological studies show that, in general, all the members of a complementation group show similar changes in muscle structure and that these changes are distinctive for that group. In mutants of several genes, disorganization of the myofilament lattice is general with no one component of the lattice more obviously altered than others. In mutants of other genes specific structures are prominently altered. In one of the instances where thick filaments appear to be abnormal, double mutants combining mutations in this gene (unc-82 IV) with mutations in the gene for a myosin heavy chain (MacLeod et al., 1977a,b) or paramyosin (Waterston et al., 1977) were used to show that the unc-82 gene product probably affects thick filament assembly through its actions on paramyosin. Some possible implications of the morphological features of the mutants as well as the conclusions derived from the genetic studies are discussed.     

Rescue of Temperature-sensitive Poliovirus

A temperature-sensitive strain of type 1 poliovirus, LSc, was functionally rescued when infected cells were incubated at 40 C in the presence of Mahoney, a temperature-resistant strain of type 1 poliovirus. The rescue value was 9% of the mutant yield obtained under permissive conditions. Rescued virus underwent replication, because the progeny of (32)P-labeled LSc were not radiosensitive. Serum inactivation studies with Mahoney specific antiserum indicated that a small amount of phenotypic mixing occurred among the rescued particles. The temperature-sensitive event occurred between 2 and 4 hr postinfection in the developmental cycle of LSc. Neither viral polymerase activity nor virus-induced ribonucleic acid could be demonstrated in infected cells between 2 and 4 hr after infection at 40 C with the temperature-sensitive mutant.     

Vesicular stomatitis virus defective interfering particles can contain extensive genomic sequence rearrangements and base substitutions

We sequenced the 5' and 3' RNA termini of 16 defective interfering (DI) particles of vesicular stomatitis virus (VSV) isolated at intervals from persistent infections and from a series of undiluted lytic passages. All DI RNAs exhibited complementary termini, but sequences internal to these termini were extensively rearranged in a variety of ways. Despite extensive rearrangement, these internal sequences (in addition to the termini) apparently are important for DI particle interference properties. Some of these DI particles are derived from multiple intrastrand and interstrand recombination events, and the generation of each can be explained by current replicase error models. During viral evolution in persistent and acute infections, DI particles with specific termini base substitutions are selected. One DI particle exhibits a remarkable clustering of specific A----G (and complementary U----C) substitutions, apparently as a result of repetitive misincorporations by an error-prone viral polymerase complex.     

Lactoperoxidase haem, an iron-porphyrin thiol.

The haem prosthetic group of lactoperoxidase can be prepared from the enzyme in high yield by reductive cleavage with mercaptoethanol in 8 M-urea under mild conditions. The product yields porphyrins, after removal of iron, which show visible spectroscopic properties similar to protoporphyrin but are considerably more polar. In the presence of iodoacetamide, a different product is obtained by reductive cleavage. The proton n.m.r. and mass spectra of this compound indicate that the prosthetic group of the enzyme is the iron complex of 18-mercaptomethyl-2,7,12-trimethyl-3,8-divinylporphyrin-13,17-d ipropionic acid. It is proposed that the unusual strength of binding of the prosthetic group to the apoprotein is due to formation of a disulphide bond from a cysteine residue to the porphyrin thiol.     

Exclusion chromatography of concentrated hemoglobin solutions: Comparison of the self-association behavior of the oxy and deoxy forms of the α2β2 species

Theory pertaining to the interpretation of partition chromatography results obtained with self-associating protein systems studied at high total concentrations is extended to permit consideration of situations in which both monomeric and dimeric states partition. This development, which includes considerations of thermodynamic nonideality effects, permits a quantitative correlation of human oxyhemoglobin results reported previously and obtained in this work employing a different stationary matrix of controlled-pore glass beads. The two sets of results, obtained at pH 7.3 and 20°C- indicate that the α₂β₂ species of oxyhemoglobin self-associates. Two types of association pattern, discrete dimerization and an indefinite self-association, are examined. This is done for a realistic range of values for the radius, r, of the effective hard sphere appropriate to the calculation of the covolume of the α₂β₂ species in the assessment of the thermodynamic nonideality contribution. Assessed values of the isodesmic association constant range from 66 = 23 M ^?1(r = 2.84 nm) to 154 = 26 M^?1' (r = 3.13 nm). This mode of indefinite association is marginally favored over a dimerization when the larger value of r is considered, the two patterns becoming virtually indistinguishable for the lower value of r. Partition chromatography results are also presented for human deoxyhemoglobin up to a total concentration of 225 $\text{g}\text{I}$, and are analyzed in a similar fashion to show that the indefinite self-association pattern is favored, governed by an isodesmic constant in the range 91 = 9 M^?1(r = 2.84 nm) to 223 = 84 M^?1 (r = 3.13 nm). Comparison of the constants assessed for the oxy and deoxy systems permits discussion of the concept that oxygen binds preferentially to the α₂β₂ species of deoxyhemoglobin in comparison with its polymers.