Physical Studies on DNA From “Primitive” Eucaryote

Size of the Chloroplast Genome in Codium fragile

Chloroplasts isolated from the siphonous green alga Codium fragile yield circular DNA molecules averaging 27.3 micrometers in length and 56 x 10(6) daltons in molecular size. This chloroplast genome is 25 to 30 percent smaller than any reported. The small size of the Codium chloroplast genome may represent a primitive evolutionary condition in green plants.

Preembryo research: medical aspects and ethical considerations

Recent advances in the field of reproduction have made it possible to obtain preembryos and to use them in many research applications. These include research into improving methods of IVF treatment, contraceptive research, preimplantation diagnosis, gene therapy, the study of malignant disease, and others. The benefits, academic and scientific, are enormous, but many moral and ethical issues and reservations exist. Potential sources from which the preembryos may originate may also lead to controversy. Pressure groups in various societies seek to hasten governments into legislation or other means of control. We conducted a MEDLINE search of all pertinent literature since 1980, and these findings have been reviewed.

Characterization of satellite DNA in Trypanosoma brucei and Trypanosoma cruzi

We have determined the properties of the simple-sequence satellite DNAs from two protozoa, Trypanosoma brucei and Trypanosoma cruzi. The T. brucei satellite DNA contains 29 mol% guanine plus cytosine and is made up of long tandem arrays of a 177 base-pair repeat. Sequence heterogeneity in these repeats is limited and restricted to certain positions as shown by sequence analysis, restriction enzyme digestion and two-dimensional analysis of nucleotides bordering the AluI and HhaI recognition sites in the repeat. The repeat contains two copies of a 19 base-pair sequence differing by a single base-pair substitution and several additional copies of part of this sequence. Sequence variants of the repeat are clustered in the DNA. Satellite DNA is not detectably linked to other DNA and no transcripts of this DNA are found in T. brucei. The T. cruzi satellite DNA repeat is 196 base-pairs long and contains 53 mol% guanine plus cytosine. Direct repetitions longer than eight base-pairs were not observed in the nucleotide sequence of this repeat. The nucleotide sequences of the satellites of T. brucei and T. cruzi are not related. In cell fractionation experiments, the T. brucei and T. cruzi satellite DNAs were recovered from the nuclear fraction. Micrococcal nuclease digestion of nuclear fractions yielded 193 and 197 base-pair nucleosomal oligomers in T. brucei and T. cruzi, respectively; these oligomers contained satellite DNA but not the extranuclear kinetoplast DNA. The 193 base-pair nucleosomal repeat of T. brucei is significantly different from the 177 base-pair satellite repeat. Satellite and nucleosomal repeats are, therefore, not in phase in T. brucei. These satellite DNAs are the first to be observed in protozoa, and we conclude that their properties are similar to those of satellites from animals or plants.

Reexamination of the genome size of myxobacteria, including the use of a new method for genome size analysis

The genome sizes of two myxobacteria, Myxococcus xanthus and Stigmatella aurantiaca, were measured by renaturation analysis and also by a new method involving the quantitation of individual restriction fragments. In contrast to several previous reports, which indicate that M. xanthus has a genome size which is three to four times that of Escherichia coli, the present measurements indicated that the M. xanthus genome is only about 24 to 53% larger than that of E. coli. S. aurantiaca had a genome size nearly identical to that of M. xanthus. Of possible significance is the fact that the renaturation curves of M. xanthus and S. aurantiaca deoxyribonucleic acid both exhibited significant fractions which renatured with rapid, unimolecular kinetics. However, we were unable to establish that these fractions represented inverted repeats of repetitive sequences.

Selfish genes, the phenotype paradigm and genome evolution

Natural selection operating within genomes will inevitably result in the appearance of DNAs with no phenotypic expression whose only 'function' is survival within genomes. Prokaryotic transposable elements and eukaryotic middle-repetitive sequences can be seen as such DNA's and thus no phenotypic or evolutionary function need be assigned to them.