NonDarwinian evolution of protein and DNA, comparing expectations of evolution models for protein and amino acid changes

http://science.sciencemag.org/content/sci/164/3881/788.full.pdf

Non-Darwinian Evolution

Biochemical and genetic studies have produced a vast fund of knowledge concerning gene action and regulation in prokaryotes In these organisms the DNA is exposed rather nakedly to the world, protected primarily by the cell membrane In eukaryotes the DNA seems far better shielded, being enmeshed in histone and nonhistone proteins and sequestered behind both the cell and the nuclear membrane These differences have led to a considerable degree of caution in the application of this knowledge of prokaryotes to problems of gene regulation in eukaryotes, and rightly so There are, however, several observations which suggest that higher organisms may have picked up a number of fundamental genetic tricks from their lowly predecessors It has frequently been suggested that eukaryotes must do things differently from prokaryotes, until proven otherwise It may be prudent to reverse this line of thought and suggest that they do things the came until proven different The following similarities suggest this (1) T he basic genetic dogmas concerning DNA replication, transcription, andlation are similar, (2) The genetic code is the same (3) Both systems appear to make use of cyclic AMP as a basic mediator for, humoral or diffusible, signals (4) In both systems DNA synthesis may be controlled at membranes (5) Both make use of different types of RNA polymerase and RNA polymerase cofactors (6) Recent studies of polylysine binding to chromatin suggest the eukaryotic DNA may not be so thoroughly enmeshed in Protein as once thought (7) The visualization of genes in action by electron microscopic techniques intimates that genes are spaced and read in a similar manner And finally, (8) merely because the clustering of related genes is unusual in higher organisms is no reason in itself to totally discard the promoter-operator-repressor concept as a way of regulating single structural genes This system has provided an immense amount of data concerning the manner in which proteins interact with specific DNA sequences to control the attachment and utilization of RNA polymerase It is hard to imagine that eukaryotes, being presented with such a superb mechanism for controlling DNA transcription, would totally discard it and opt for something different It is far more likely that they would build on to this solid foundation

The structure and function of chromatin.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Range of Variability of DNA Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 DNA Variation in Higher Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Gymnosperms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Angiosperms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Mechanisms of Change in DNA Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Cellular and Organismic Correlations with DNA Content . . . . . . . . . . . . . . . . . . . . . . . . 40 Functions of DNA Sequences Duplicated or Deleted during Evolution . . . . . . . . . . . . . 41 Prospects for Future Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Evolution of DNA content in higher plants

Cell Size and the Concept of Wasteful and Frugal Evolutionary Strategies

"Repetitive" DNA in higher organisms.

The nuclei of Amphiuma contain 168 pg of DNA, 28 times that contained in human nuclei. Although many higher organisms appear to possess an excessive amount of DNA, in Amphiuma this has been carried to the extreme. Studies of this organism thus may provide some insight into how this excess DNA is used. This organism presumably evolved by numerous polyploidy and gene duplication events. Do its gene products present multiple electrophoretic forms? Are they quantitatively increased to the same degree as the DNA? Electrophoresis of Amphiuma glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, acid phosphatase, lactic dehydrogenase, and hemoglobin failed to show any evidence for multiple electrophoretic forms of these respective gene products. The amount of hemoglobin, G6PD, and 6PGD per red cell was increased to a comparable or even greater degree than the DNA. Analytical ultracentrifugation demonstrated a satellite band of DNA with a density of 1.720 corresponding to a GC content of 61%. This probably represents DNA coding for ribosomal RNA. Electron microscopy of liver nuclei showed a significant amount of condensed chromatin. The implications of these observations are discussed.

Ronald O. Berger

Papers

Gene Products of Amphiuma: An Amphibian with an Excessive Amount of DNA