Glossary

PCR
  Polymerase chain reaction, is a reaction catalyzed by the enzyme Taq polymerase, which amplifies DNA fragments for sequencing or other purposes.

Read
  This term designates a single sequencing operation as well as the information it delivers, i.e. a sequence which is 800-1000 bases long, generally from one of the extremities of a longer DNA fragment.

Restriction enzymes
  Enzymes which are capable of cutting DNA molecule at the sites of specific sequences. There are more than 400 of these, which recognize sequences from 4 to 8 bases in length. The longer sequences are the least frequent in the genome, and the enzymes which recognize these sites can cut the DNA into large fragments. Restriction enzymes are also used to establish specific “profiles” of large fragments (fingerprints). Comparison of these profiles is used to identify overlapping fragments.

RNA
  Ribonucleic acid is a molecule which is very similar to DNA, but consists of a single chain of nucleotides. The instructions encoded in the DNA sequence are copied (“transcribed”) into a type of RNA called messenger RNA, for translation into proteins, which are the real agents of cellular functions. These RNA molecules are also called transcripts.

Sequence, sequencing
  Sequencing is the operation which consists of determining the order, or sequence, of the bases along the DNA molecule. A sequence looks like a text of variable length, written with an alphabet of only 4 letters, A, T, C and G (see Base). Genoscope determined the order of the 87 million letters of the uninterrupted sequence of human chromosome 14.

Template
  The templates are DNA molecules which contain an insert to be sequenced, which has been extracted and purified from a bacterial clone. They are then ready to be used in sequencing reactions or PCR.

Transformation
  An operation which consists of using a vector to insert a DNA sequence which it contains into a bacterium in order to clone this sequence (insert). Very brief electric shocks are used for this purpose today, with good efficiency.