Gene synthesis review

The concentration of mRNA available for translation is determined by the de novo synthesis, as well as by the degradation rate. The specific degradation of mRNAs plays an important role in cell- and tissue-specific gene expression (review Sachs, 1993). The stabUity of various mRNAs can vary significantly from 20 min to 24 hour half-life in the same cell. 

Synthesis of Genes by Polymerase Chain Reaction. Another strategy that takes advantage of specific oligonucleotide primers is the in vitro amplification of specific DNA fragments from very small amounts of an impure sample. Since the first demonstration of the technique by Mullis and Faloona (57) it has become one of the most popular procedures in molecular biology and virtually has transformed our approach to isolation of genes [for review see (58-60). 

Gene synthesis is the step during which oligonucleotides (oligos) are combined into DNA fragments of several hundred bases in length. Numerous protocols have been described and extensively reviewed, including polymerase chain assembly (PCA), thermodynamically balanced inside-out synthesis (TBIO) (2), and... 

Non-neuronal transplants such as adrenal chromaffin cells have been tried but do not survive although some L-dopa-producing cell lines (e.g. PC 12) or glomus cells of the carotid body do produce DA in vivo and may provide the equivalent of a continuous infusion of dopa (and DA) directly into the brain. Expression of tyrosine hydroxylase to promote dopa and DA synthesis in striatal cells by direct gene transfer in vivo or in cultures for subsequent transplanting, may also be possible. (See Dunnett and Bjorklund 1999 for a review of these approaches.)... 

Several independent laboratories have now demonstrated that both lithium and valproate (VPA) exert complex, isozyme-specific effects on the PKC (protein kinase C) signaling cascade (reviewed in [3, 5, 11-13]). Not surprisingly, considerable research has recently attempted to identify changes in the activity of transcription factors known to be regulated (at least in part) by the PKC signaling pathway - in particular the activator protein 1 (AP-1) family of transcription factors. In the CNS, the genes that are regulated by AP-1 include those for various neuropeptides, neurotrophins, receptors, transcription factors, enzymes involved in neurotransmitter synthesis, and proteins that bind to cytoskeletal elements [14]. 

With a morphine biosynthetic gene in hand, we believed we could begin to address the question why only P. somniferum produces morphine, while other Papaver species such as P. rhoeas, P. orientale, and P. bracteatum do not. Unexpectedly, we found that the codeinone reductase transcript was present to some degree in all four species investigated. A review of the literature revealed no alkaloids reported in P. rhoeas for which codeinone reductase should participate in the synthesis. Similarly, P. orientale accumulates the alternate morphine biosynthetic precursor oripavine, but codeinone reductase is not involved in the biosynthesis of oripavine, acting instead after this alkaloid along the biosynthetic pathway to morphine.22 P. bracteatum produces the morphine precursor thebaine as a major alkaloid. As for oripavine in P. orientale, codeinone reductase would act in P. bracteatum after thebaine formation on the pathway to morphine. It appears, therefore, that the reason that P. rhoeas, P. orientale, and P. bracteatum do not produce morphine is not related to the absence of the transcript of the morphine biosynthesis-specific gene codeinone reductase. The expression of codeinone reductase may simply be an evolutionary remnant in these species. 

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