Biochemistry - The Chemical Reactions of Living Cells, Volume 3 - D. Metzler 1980

Biochemical Genetics and the Synthesis of Nucleic Acids and Proteins
Mutations, Cancer, and Genetic Engineering
Gene Surgery

Our current understanding of the mechanisms of Gene action and regulation, alongside the potential for partial DNA transfer from one bacterium to another, opens up the prospect of correcting genetic defects by introducing new genes into humans. At first glance, this idea might seem purely fanciful; however, we already know of Viruses such as SV40 that are capable of integrating into animal genomes. Although the SV40 virus is oncogenic by nature, there is hope that we might obtain SV40-like DNA particles carrying "normal" genes extracted (perhaps with the help of other viruses) from cultured Cells. Another possible approach is to isolate genes from Bacteria, or to introduce chemically synthesized genes into transducing viruses.

Practical chemical Methods have been developed that make it possible to join chromosome fragments [258, 259]. One approach involves using Restriction Endonucleases to generate DNA fragments with sticky ends. Eukaryotic genes have already been successfully incorporated into bacterial R-factors, and SV40 genes into phage λ [260]. Similarly, gal Operon genes of E. coli have been integrated into the SV40 virus genome using phage λ. An important feature of these methods is that they rely on "molecular cloning" of novel DNA combinations incorporated into a bacterial plasmid [261]. Plasmids capable of Replication in E. coli cells have been employed for this purpose.

Few doubt nowadays that artificial Gene Insertion into human cells is achievable; however, our understanding of how gene METABOLISM/31.html">Transcription and Translation are controlled in animals remains limited. Future research will undoubtedly shed light on The Nature of this regulation, potentially paving the way for successful "gene surgery." One specific goal of this approach could be finding ways to correct the metabolic defects responsible for the destruction of Insulin-secreting pancreatic ß-cells in juvenile-onset diabetes. The number of patients who could benefit from such Treatment is extraordinarily large (Supplement 11-B).

Evidence suggests that transducing Bacteriophages can transfer bacterial genes into cells while retaining their capacity for phenotypic expression [261–263]. Data have even been obtained showing that DNA can integrate directly into plant cells (much like Bacterial Transformation, Section A.1) [264]. Such a capability could revolutionize plant breeding. Of tremendous interest is the prospect of transferring nitrogen-fixation genes (from Rhizobium-like bacteria) into higher plant cells. A major stepping stone toward this goal has been the successful transfer of the Nitrogenase operon (nif) genes from Klebsiella into E. coli cells [263–266]. The feasibility of transferring genes Cell/4.html">From Prokaryotes to eukaryotes currently remains somewhat ambiguous. Nevertheless, evidence exists for the successful transfer of a gene required for Histidine Biosynthesis (the imidazoleglycerol-phosphate dehydratase gene; Fig. 14-28) from Yeast to a histidine-auxotrophic strain of E. coli, with the gene retaining its phenotypic expression [266a].

Biologists often hold the view that mankind will eventually learn to control its own genes and prevent Genetic Disorders caused by the accumulation of deleterious Mutations. They look forward with enthusiasm to the day when humans might direct their own evolution along a desired path [267]. However, some biologists urge caution, arguing that our knowledge is still insufficient and that attempts to eradicate all "bad" genes from a population could lead to unforeseen consequences [268]. As an example, they point to the Hemoglobin S gene (Supplement 4-G), which, although defective, once protected individuals from dying during malaria epidemics. They contend that the only viable approach to Selection at present is to maximize genetic heterogeneity. Proponents of this view draw attention to the inherent dangers of geneticists intervening in human life. In the past, eugenic doctrines were regrettably used to justify and enforce racist laws and genocide (in Nazi Germany).

Nevertheless, the challenges associated with the accumulation of harmful mutations in humans cannot be ignored. As new genetic defects are identified, an increasing number of individuals face the difficult choice of whether to have children. Fortunately, prenatal Diagnosis provides the option to decide between terminating a Pregnancy or caring for a severely disabled child throughout life (Chapter 12, Section D-2). Yet, this approach carries its own perils. Even if abortion were to become widely accepted, it is frightening to contemplate a society in which amniocentesis became mandatory.

Other, more immediate hazards exist. In 1974, the U.S. National Academy of Sciences' Committee on Recombinant DNA Molecules called for a moratorium on experiments in two specific areas that could pose risks to humanity as a whole [269]. The committee emphasized that using E. coli to clone recombinant molecules could be hazardous, as these bacteria inhabit the human gut and can exchange Genetic information with human pathogens. The committee recommended voluntarily refraining from the two highlighted lines of research, which might lead to the accidental incorporation into Chromosomes of genes conferring Antibiotic Resistance, toxin production, or tumor formation. Particular warnings were issued regarding any plans to link animal DNA fragments with the DNA of bacterial plasmids or phages. Oversight of such research is expected to be maintained by various funding agencies that support biochemical studies [269].