Recombinant DNA technology

Intron-Mediated Enhancement: A Tool for Heterologous Gene Expression in Plants?

Many plant promoters were characterized and used for transgene expression in plants. Even though these promoters drive high levels of transgene expression in plants, the expression patterns are rarely constitutive but restricted to some tissues and developmental stages. In terms of crop improvement not only the enhancement of expression per se but, in particular, tissue-specific and spatial expression of genes plays an important role. Introns were used to boost expression in transgenic plants in the field of crop improvement for a long time. However, the mechanism behind this so called intron-mediated enhancement (IME) is still largely unknown. This review highlights the complexity of IME on the levels of its regulation and modes of action and gives an overview on IME methodology, examples in fundamental research and models of proposed mechanisms. In addition, the application of IME in heterologous gene expression is discussed.

Kinetic analysis for optimization of DNA ligation reactions

Kinetic equations describing ligation of DNA to circular recombinant forms were developed and solved for four types of reactions: (a) a homogeneous population of singly restricted DNA fragments, (b) insertion of singly restricted insert into vector, (c) forced directional insertion of doubly restricted insert into vector, and (d) insertion of singly restricted insert into phosphatased vector. The effects of varying vector and insert sizes, starting concentrations, and phosphatase treatment on the yield of circular 1:1 recombinants were analyzed. Selected theoretical predictions were experimentally tested and verified. Our suggestions on optimizing ligation reactions in several cases are at variance with common practice. For example, optimum conditions in case (b) and (d) ligations are best specified as individual insert and vector concentrations rather than as insert/vector molar ratios, except in case (d) ligations involving very small insert size. In case (c) ligations, highest efficiencies are obtained when both vector and insert are at relatively low concentration.