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RNA Transcription

Transcription refers to the transfer of genetic code information from one kind of nucleic acid to another and to the process by which a base sequence of messenger RNA is synthesized by an RNA polymerase on a template of complementary DNA. A polymerase associated with the process of transcription is called a "transcriptase". The DNA-dependent RNA polymerase is an example for a transcriptase. The template is defined as "a single-stranded polynucleotide or the region of a polynucleotide that directs the synthesis of a complementary polynucleotide". Experiments that aim to find out which portion of a DNA molecule is transcribed into RNA are called "transcript analysis", and the entire mRNA content of a cell or tissue is now called the "transcriptome". SP6, T7 and T3 phage RNA polymerases have high specificity for their respective base promoters. Due to the development of cloning vectors containing promoters for these polymerases the in vitro synthesis of single stranded RNA molecules is now a routine laboratory procedure. Sense or antisense RNAs can now also be synthesized either automatically using standard phosphoramidite chemistries or from sequences cloned into multiple cloning sites. Linearized plasmid sequences, PCR products and synthetic oligonucleotides can be used as templates for transcription reactions, the template need only be single stranded. In vitro transcription reactions are generally used for the synthesis of highly specific activity RNA probes and the synthesis of larger quantities of RNA. Large amounts of RNA are needed for in vitro translation, microinjection, ribozyme studies, microarray analysis, non-radioisotopic probes, the synthesis of high specific activity probes for use in ribonuclease protection assays, Northern and Southern blotting and in situ hybridizations, and a variety of other applications.

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