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Complementary DNA (cDNA) is a DNA copy produced by reverse transcription of a messenger RNA (mRNA) molecule. mRNA generally consists of untranslated regions (UTRs) and translated coding regions. cDNAs mirror the native RNA sequence. A full-length cDNA clone must contain the complete open reading frame (ORF) and typically contains part of or all the 5' and 3' UTRs. ORFs are derived from cDNA by removing the UTRs and leaving the protein coding sequence. Non-coding regions are removed and replaced with flexible cloning sites, so ORFs show increased flexibility when transferring to expression vectors. This facilitates a variety of experiments, such as tracking subcellular localization, protein-protein interaction studies, or antibody production. Upstream ORFs (uORFs) are cis-elements in the 5’ UTRs of the mRNA and can be translated to functional peptides. uORFs have multiple properties, including promoting ribosome re-initiation after uORF translation, ribosome elongation stalling during uORF translation, ribosome dissociation from the mRNA, ribosome translation of uORFs past the coding sequence start codon. Most uORFs negatively regulate the expression of protein encoding main ORF of mRNA.

Amerigo Scientific offers an extensive library of sequence verified ORFs from human, mouse and rat that are used for insertion into target expression systems. Without the UTRs, ORFs allow for rapid and reliable protein expression when inserted into compatible expression vectors. These ORFs can also be used as a template for positive control in PCR amplification experiments.