The poly(a) tail is a feature on eukaryotic mRNA, which is composed of multiple adenylates and is located at 3 of mRNA'End. Poly(a) tails play an important role in the regulation of gene expression, especially in translation and control of mRNA stability. The polya tail at the end of mRNA 3' prevents exonuclease from pairing mRNA 3'Degradation of the ends, increasing the stability of mRNA. In addition, polya acts as a "translation enhancer" during the translation process. Studies have shown that removal of the polyA site reduces mRNA expression levels by up to 10-fold. The polya tailing signal requires 3 parts: the polyadenylation signal sequence 5'-aauaaa-3'; splice sites and tail sites ya; Downstream conserved sequences, such as u-rich or (g+u)-rich.
In addition to the polya tailing signal, eukaryotic gene expression vector elements also include selective marker genes and reporter genes
Selective marker genes are important components of expression vectors and typically encode an enzyme that is not present in normal cells. Although a small number of transformed cells can be separated from untransformed cells under selection pressure, the application of selection marker genes also has its own insurmountable drawbacks. For example, when a transformed cell already contains a resistance gene as a marker gene, a different selection marker gene is used when introducing a second exogenous gene, and the actual application of the selection marker gene is very limited. In addition, from a health and safety perspective, select marker genes and their products may be toxic or allergenic when used. Therefore, in transgenic transgenics, the removal of selection marker genes is conducive to improving the food safety and environmental safety of transgenes, and multiple transgenic operations can also be performed on the same recipient cell. At present, some transformation techniques have been developed to remove selection marker genes, such as site-specific recombination system, tissue-specific expression of selection marker genes, co-transformation, repositioning of transferred genes in the genome and target gene replacement through transposons.
The reporter gene mainly plays the role of reporter and recognition, and its expression product is non-toxic to the recipient cell, which can reflect the expression level of the foreign gene in the recipient cell.