Repetitive sequences of the sea urchin genome: Distribution of members of specific repetitive families

Three repetitive sequence families from the sea urchin genome were studied, each defined by homology with a specific cloned probe one to a few hundred nucleotides long. Recombinant λ-sea urchin DNA libraries were screened with these probes, and individual recombinants were selected that include genomic members of these families. Restriction mapping, gel blot, and kinetic analyses were carried out to determine the organization of each repeat family. Sequence elements belonging to the first of the three repeat families were found to be embedded in longer repeat sequences. These repeat sequences frequently occur in small clusters. Members of the second repeat family are also found in a long repetitive sequence environment, but these repeats usually occur singly in any given region of the DNA. The sequences of the third repeat are only 200 to 300 nucleotides long, and are generally terminated by single copy DNA, though a few examples were found associated with other repeats. These three repeat sequence families constitute sets of homologous sequence elements that relate distant regions of the DNA.     

Introduction of cloned DNA into sea urchin egg cytoplasm: replication and persistence during embryogenesis

Cloned DNA sequences were introduced into the cytoplasm of unfertilized sea urchin eggs by a simple microinjection technique. Sperm was then added, and development allowed to proceed. If linearized plasmids are injected they form random concatenates, and during the early development of the embryos replicate repeatedly. Eukaryotic sequences are not required for replication of the exogenous DNA. Injected supercoiled DNAs neither ligate nor replicate. Both forms of exogenous DNA persist in the embryo through pluteus stage.     

The Synthesis of Ribosomes in E. coli: I. The Incorporation of C14-Uracil into the Metabolic Pool and RNA

C¹⁴-uracil is rapidly incorporated by E. coli at low concentrations. Approximately half the radioactivity passes directly into RNA with very little delay. The remaining half enters a large metabolic pool and later is incorporated into RNA. The total rate of uptake (growing cells) is not greater than the requirement for uracil and cytosine for RNA synthesis. The size of the metabolic pool is not influenced measurably by the external uracil concentration. No evidence is found for the existence of a fraction of RNA which is rapidly synthesized and degraded.     

Interactions ofCandida albicans with bacteria and salivary molecules in oral biofilms

The yeastCandida albicans coaggregates with a variety of streptococcal species, an interaction that may promote oral colonization by yeast cells.C. albicans andCandida tropicalis are the yeasts most frequently isolated from the human oral cavity and our data demonstrate that both these species bind toStreptococcus gordonii NCTC 7869 while two otherCandida species (Candida krusei andCandida kefyr) do not. Adherence ofC. albicans was greatest when the yeast had been grown at 30° C to mid-exponential growth phase. For 21 strains ofC. albicans there was a positive correlation between the ability to adhere toS. gordonii and adherence to experimental salivary pellicle. Whole saliva either stimulated or slightly inhibited adherence ofC. albicans toS. gordonii depending on the streptococcal growth conditions. The results suggest that the major salivary adhesins and coaggregation adhesins ofC. albicans are co-expressed.     

Studies on nucleic acid reassociation kinetics: V. Effects of disparity in tracer and driver fragment lengths.

Measurements are described of the kinetics of nucleic acid strand pair reassociation where the complementary strands are of different lengths and are present in different concentrations. Rate constants for the reaction of labelled fragments ("tracer") with excess complementary strands ("driver") were determined, both for driver fragment length greater than tracer fragment length and for the reverse case. Second order reactions and pseudo-first order reactions utilizing strand separated drivers and tracers were studied. The nucleic acids which served for this investigation were phiX174 DNA and RNA, plasmid RSF2124 DNA and E. coli DNA. Approximate empirical expressions relating driver and tracer fragment lengths with the observed rate constants were obtained for practical use. In long tracer-short driver reactions the observed rate constant for the tracer reaction increases proportionately with tracer length. In long driver-short tracer reactions the rate of tracer reaction is retarded. The latter result is unexpected and appears to represent a departure from standard interpretations of the renaturation reaction.