15. 1 dna cloning mrna transcript isolated from sample of cells that express gene of interest o o o. Reverse transcriptase: catalyzes the assembly of complimentary dna strand on mrna transcript. Enzymes removed mrna to produce single stranded cdna. Double stranded cdna synthesized: using dna strand as template cdna. Bacterium: can use cdna to express gene of interest o. Because eukaryoic mrna transcript has introns removed, cdna of gene does not have introns, making it easier for proper protein to be produced in bacterial cells. 3 main sources of dna sequences commonly used in research o o o. Dna sequences can be extracted from the genome of cells (and viruses) using specialized enzymes. Dna can be synthesized from mrna template by reverse transcriptase. Dna sequences of choice can be created by automated chemical synthesis in the laboratory using a dna synthesizer responding to computer input.