ABSTRACT
Polymerases usually require a particular arrangement of double-helical nucleic acid. By direct chemical analysis of purified proteins, it has been shown that they are composed of linear polymers of amino acids, referred to as polypeptides. These polymers are formed by a ribosome that reads the messenger RNA and converts the sequence of codons into a sequence of amino acids coupled covalently together in the dictated order. The particular sequences of nucleotides and the associated points of cleavage are known as restriction sites, and the fragments of DNA produced by these cleavages are known as restriction fragments. Polypeptides are synthesized biologically by ribosomes that translate the sequence of nucleotides in a single-stranded messenger RNA into a sequence of amino acids in a polypeptide. A piece of DNA encoding another amino acid sequence is often inserted ahead of the DNA encoding the protein of interest.
