Natural Mutagenesis

Unfortunately, die well-known saying that the new is the once forgotten old relates also to scientific matters. In 1988, French autiiors (Naud et al., 1988) reported that natural mutants arose in populations of P. freuden-reichii placed imder harsh conditions permitting no growth or subjected to UV shock. The mutants of a spherical shape differed from the original rodlike cells in many properties, which will be discussed in detail below. 

The facts, reported by these authors, made us to return to our almost forgotten results from the late 1960s (Vorobjeva and Baranova, 1969) that also concerned the natural genetic variabihty of propionic acid bacteria. In those years some microbiologists in Russia were unreceptive to the facts given below, since they did not conform to the established view of propionic acid bacteria. But now these data may have a considerable scientific and practical interest. 

Lactate-peptone agar Lactate-peptone agar (dried plates) 

However, if cells pretreated as above were inoculated into a medium without antibiotics, colonies of the rodlike cells reappeared, reversing into the original, non-induced state. Therefore, P. freudenreichii strain El behaved as a natural mutant. No mutagenesis was used to induce this strain, and the high yield of spherical forms excluded completely the involvement of mutational mechanisms. 

Interestingly, the generation time (g) of the spherical form growing under aerobic conditions was 2 h, and that of the original form was 4.5 h. Under anaerobic conditions both strains grew at the same rate (g = 4.5 h), which shows that the spherical form is better adapted to the aerobic style of life (similar to the apigmented strain in our investigations). In contrast with the 

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Natural selection works through the complementary processes of mutation and genetic reassortment by recombination. The oligonucleotide-directed mutagenesis methods used in the foregoing examples do not allow for recombination instead, mutations are combined manually to optimize a protein sequence. Willem Stemmer at Maxygen invented a method of directed evolution that uses both mutation and recombination. This method, called... 

Carrano AV, Thompson LH, Lindl PA, et al. 1978. Sister-chromatid exchange as an indicator of mutagenesis. Nature 271 551-553. 

Baltimore D (1988) Gene therapy. Intracellular immunization. Nature 335 395-396 Basta S, Stoessel R, Easier M, van den Broek M, Groettrup M (2005) Cross-presentation of the long-lived lymphocytic choriomeningitis virus nucleoprotein does not require neosynthesis and is enhanced via heat shock proteins. J Immunol 175 796-805 Baum C (2007) Insertional mutagenesis in gene therapy and stem cell biology. Curr Opin Hematol 14 337-342... 

KASSIE F, PooL-zoBEL B, PARZEFALL w and KNASMULLER s (1999) Genotoxic effects of benzyl isothiocyanate, a natural chemopreventive agent . Mutagenesis, 14 595-604. 

The development of a commercially viable algal astaxanthin process requires both an effective closed culture system and a selection (from Nature or via mutagenesis) of strains of Haematococcus with higher astaxanthin contents and abilities to tolerate higher temperatures than the wild strains. 

While the ddNs and ANPs must be converted intracellularly to their 5 -triphosphates (ddNTPs) or diphosphate derivatives before they can interact as competitive inhibitors/alternate substrates with regard to the natural substrates (dNTPs), the NNRTIs do not need any metabolic conversion to interact, noncompetitively with respect to the dNTPs, at an allosteric, non-substrate binding site of the HIV-1 RT. Through the analysis of NNRTI-resistant mutants, combined with site-directed mutagenesis studies, it has become increasingly clear which amino acid residues are involved in the interaction of the NNRTIs with HIV-1 RT, and, since the conformation of the HIV-1 RT has been resolved at 3.0 A resolution [73], it is now possible to visualize the binding site of the NNRTIs [74],... 

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