What about cloning RNA? [cDNA is 'complementary' DNA]

This is important because the RNA from eukaryotes will have a sequence co-linear with the protein sequence, whereas the DNA will have extra sequence from introns. The mRNA of eukaryotes is easy to isolate (well, relatively easy) since it has a 3' poly-dA sequence. After extracting total RNA, the RNA is passed over a column with oligo-dT attached to the solid support. This column will selectively bind to the mRNA and it can be washed off the column by denaturing the poly-dA/oligo-dT complementary sequences.

The mRNA cannot be cloned directly into a plasmid because mRNA is not double stranded and is not chemically stable. The ss-mRNA is mixed with an oligo-dT primer, the 4 dNTPs and reverse transcriptase. This synthesizes [local] a mRNA-DNA hybrid. Since the DNA strand is complementary to the RNA, it is termed cDNA.

The mRNA-DNA hybrid is incubated with RNase H to hydrolyze the RNA strand, leaving ss-DNA.

The ss-DNA is incubated with the 4 dNTPs and DNA Polymerase I. The bits of RNA which survive the digestion with RNase H act as primers and the DNA Polymerase I synthesizes a new DNA strand complementary to the ss-DNA template in a fashion similar to Okazaki fragments on the lagging strand during replication. This completes the synthesis of a ds-DNA.

Once the ds-DNA is synthesized, it can be cloned into a plasmid vector by blunt-end ligation which is inefficient. It could have oligonucleotides with restriction endonuclease sites ligated on to the ends, followed by treatment with the appropriate restriction endonuclease. This will create sticky ends for cloning into restriction sites in plasmids.

This site [local] has more information than you need at this time, so only read the sections that seem appropriate.