(cDNA) is a doublestranded DNA version of an
mRNA molecule. In higher eukaryotes, an mRNA is
a more useful predictor of a polypeptide
sequence than is a genomic sequence, because the
introns have been spliced out. Researchers
prefer to use cDNA rather than mRNA itself
because RNAs are inherently less stable than DNA
and techniques for routinely amplifying and
purifying individual RNA molecules do not exist.
The cDNA is made
from mRNA with the use of a special enzyme
called reverse transcriptase, originally
isolated from retroviruses. Using an mRNA
molecule as a template, reverse transcriptase
synthesizes a single-stranded DNA molecule that
can then be used as a template for
double-stranded DNA synthesis.
does not need to be cut in order to be cloned.