L

LATE (Linear After The Exponential)-PCR:

A new form of asymmetric PCR that uses primer pairs deliberately designed for use at unequal concentrations. Unlike typical asymmetric PCR, LATE-PCR, amplification is efficient due to improved primer design. LATE-PCR begins with an exponential phase in which amplification efficiency is similar to that of symmetric PCR.

Leucine zipper:

A motif found in certain proteins in which Leu residues are evenly spaced through an a-helical region, such that they would end up on the same face of the helix. Dimers can form between two such proteins. The Leu zipper is important in the function of transcription factors such as Fos and Jun and related proteins.

Leader sequence:

Two usages;

1] N-terminal pre sequence of scretory proteins such as peptide hormones and membrane proteins.

2] The untranslated sequence at the 5'-ends of mRNA molecules.

Leucine zipper:

A motif found in certain proteins in which Leu residues are evenly spaced through an a-helical region, such that they would end up on the same face of the helix.

Library:

A library might be either a genomic library, or a cDNA library. In either case, the library is just a tube carrying a mixture of thousands of different clones - bacteria or l phages. Each clone carries an "insert" - the cloned DNA.

Ligase:

An enzyme, T4 DNA ligase, which can link pieces of DNA together. The pieces must have compatible ends (both of them blunt, or else mutually compatible sticky ends), and the ligation reaction requires ATP.

Ligation:

The process of splicing two pieces of DNA together.

Light-up probe:

The light-up probe is a peptide nucleic acid (PNA) oligomer to which an asymmetric cyanine dye thiazole orange (a single reporter dye) is tethered.

Linker:

A small piece of synthetic double-stranded DNA which contains something useful, such as a restriction site. A linker might be ligated onto the end of another piece of DNA to provide a desired restriction site.

Linkage:

The measure of proximity of two or more markers (e.g., genes, RFLP markers) on a chromosome determined by recombination events. The closer together the markers are, the lower the probability that they will be separated during DNA repair or replication processes (binary fission in prokaryotes, mitosis or meiosis in eukaryotes), and hence the greater the probability that they will be inherited together.

Linear Epitope:

An epitope formed by a series of amino acids which are adjacent to each other within the primary structure of the protein. Such epitopes can be successfully modelled by synthetic peptides, but comprise only a small proportion of all epitopes. The minimal epitope size is about 5 amino acid residues. Also called a sequential epitope.

Linear View:

Amplification plot view displayed using exact DRn values on the Y-axis. The alternative is the log-view, which expands the initiation of exponential amplification phase . Either can be used for threshold setting.

Linkage map:

A map of the relative positions of genetic loci on a chromosome, determined on the basis of how often the loci are inherited together. Distance is measured in centimorgans (cM).

Linker DNA:

It is the DNA contained on a nucleosome in excess of the 146bp core DNA.

Linking Number:

It is the number of times the two strands of a closed DNA duplex cross over each other.

Lipofectin:

A commercially marketed liposome suspension which is mixed with DNA or RNA to facilitate uptake of the nucleic acid by eukaryotic cells

Locked Nucleic Acid (LNA®) Probes:

A new generation of sequence-specific probes designed using LNA, which has enhanced hybridization performance and biological stability. LNA has also been used in primers to increase sensitivity.

Log-dilution:

Serial dilutions in powers of 10 (10, 100, 1000 etc).

L-chain:

Immunoglobulin light chains.

Localize:

Determination of the original position (locus) of a gene or other marker on a chromosome.

Locus (pl. loci):

The position on a chromosome of a gene or other chromosome marker; also, the DNA at that position. The use of locus is sometimes restricted to mean regions of DNA that are expressed. See gene expression.

Long(q) and short(p) arms:

The regions either side of the centromere, a compact part of a chromosome, are known as arms. As the centromere is not in the centre of the chromosome, one arm is longer than the other.

LTR (Long Terminal Repeat):

A sequence directly repeated at both the ends of a retroviral DNA.

Lysogeny:

It describes the ability of a phage to survive in a bacterium as a stable prophage component of the bacterial genome.