Mosaic
1. An embryo or organism in which all cells do not carry identical genes. 2. A transgenic animal in which the transgene is present in only a proportion of the cells or tissues.

Mosaic genes
Genes comprised of domains from different sources.

Mosaicism
The property of a tissue as a mixture of clonal populations of cells. According to the Lyon effect, only one X chromosome will be expressed in one cell lineage. The presence of cells with different X chromosome activated in a cell population indicates a mixture of clones. If the same X chromosome is always active. it indicates the clonal origin of tumour cells.

Mother plant
See donor plant.

Motif
A conserved element of a protein sequence  alignment that generally correlates with a specific function. A motif is generated from a local multiple protein sequence alignment that corresponds to a region whose function or structure is known. Since it is conserved, it can predict any sub sequent occurrence of such a structural/function region in any other protein sequence.

β-α-a-b motif
A supersecondary structure in proteins in which two parallel b-strands are separated by an a-helix.

Motor protein
A protein that uses the energy obtained from nucleoside triphosphate hydrolysis to move itself along a protein filament or a polymeric molecule.

mRNA
See messenger RNA.

mRNA exporter
A heterodimeric protein that binds to mRNA-containing ribonucleo-protein particles (mRNPs). It interacts with nucleoporins in the nuclear pore complex and directs the export of mRNPs from the cytoplasm to the nucleus.

mRNA surveillance
A collective term to refer to cellular mechanisms that block translation of improperly processed mRNA molecules.

MRUs
minimum recognition units. See dabs.

Msr, msd
Loci that encode an unusual RNA-DNA hybrid. The RNA transcribed from msr is covalently linked to msd DNA. This type of structure is found in myxobacteria and in the soil bacterium Stigmatella aurantiace.

mtDNA
See Mitochondrial DNA.

MTOC
See Microtubule organising center.

Mucopoly-saccharide
An older term for a glycosaminoglycan.

Mucosal-associated lymphoid tissue (MALT)
Collections of lymphoid cells found along the mucus membranes of the respiratory, digestive and urogenital tracts.

Mucoviscoidosis
Increased viscosity of pancreatic exocrine secretions.

Mucus cells A type of cells present in gastric glands that secrete gastric mucus.

MuD phage
 A variant of the bacteriophage Mu engineered as a cloning vector for determining the promoter activity using b-galactosidase as a reporter gene.

Mullis, Kary
(b.1944) An American biochemist who was awarded the Nobel Prize in Chemistry in 1993 for his development of the Polymerase Chain Reaction (PCR), a technique for selective amplification of specific DNA sequence. See PCR.

Multiadhesive matrix proteins
A group of proteins that crosslink the cell membrane to the extracellular matrix by binding to matrix components such as collagen and polysaccharides and to cell-surface receptors. Examples of such proteins are laminin and fibronectin.

Multicopy plasmids
Bacterial plasmids present in more than one copy per cell. For example, pBR322 is a multicopy plasmid, There are usually 50 copies of pBR322 per E.coli genome.

Multidimensional Protein identification Technology (MudPIT)
An unbiased method for rapid and large-scale proteome analysis via multidimensional liquid chromatography, tandem mass spectrometry, and database searching via the SEQUEST algorithm. This method can detect and identify proteins rarely seen in proteome analysis including integral membrane proteins from several cellular compartments and low abudance proteins like transcription factors and protein kinases.

Multidrug resistance (mdr) gene
A gene that confers resistance to the cytotoxic effects of chemotherapeutic drugs such as methotrexate. The mdr genes arise as a result of gene amplification and are present as homogeneously staining regions on chromosome or as extrachromosomal double minutes.

Multidrug resistance protein (MDR protein)
An ABC transporter protein that pumps hydrophobic drugs including anticancer drugs out of the cell.

Multienzyme system
A group of related enzymes that participate in a given metabolic pathway.