MATA1- Mating Type Protein A1
Alternative Names for MATA1: A1, HMRA1
MATA1 is one of four proteins involved defining a Saccharomyces cell's mating type. It is located on Saccharomyces' chromosome 3 (SGD, 2001) and is encoded by the a mating type cassette along with MATA2 (YPD, 2001). The name by which this gene is referred depends on its location. A1 can be located at the HMR locus where it is refered to as HMRA1 and is silenced (SGD, 2001). A1 can also be located at the MAT locus where it is referred to as MATA1 and is expressed (SGD, 2001). Movement of the gene on chromosome 3 in and out of the MAT locus is stimulated by a cut in the double stranded DNA at the MAT locus (Strarthem,1982), mediated by HO endonucleus (SGD, 2001), and results in the switching of the cells' mating type (SGD, 2001).
In order to understand its function, it is necessary to understand the reproduction cycle of Saccharomyces. Normally Saccharomyces reproduce through asexual budding, but when the cells are under stress two cells of opposite mating type can fuse to from a diploid cell. Saccharomyces are able to change their mating type from a1 or a2 to alpha1 or alpha2. Cells that are a mating type secrete an a-factor pheromone while cells that are alpha mating type secrete an alpha-factor pheromone.
MATA1 produces a homeodomain regulatory protein found in the nucleus (YPD, 2001). It has no known role in the production of a-specific gene expression(SGD, 2001), but is a known transcription factor that inhibits or represses cell stress responses, cell wall maintenance, mating response and possibly Pol II transcription (YPD, 2001). In diploid cells MATA1 interacts with MATalpha2 from the adjoining cell to repress haploid specific genes (SGD, 2001). MATA1 also serves as a negative regulator of STA1, STA2, STA3 which encode for 3 glucoamylase isozymes required for starch hydrolysis during G1 vegetative cell division in an environment with little fermentable sugars (YPD, 2001: Viver et.al, 1997)).
MATA1 consist of 381 nucleotides and MATA1 codes for 126 amino acids and it is predicted that there may be two forms of the protein resulting from incomplete splicing of the C-terminal (YPD, 2001).
Figure from PDB 2001- permission requested
A null mutant for MATA1 is viable, but many mutations affect cell function (YGD, 2001). Mutations in the MATA1 homeodomain (residues 2 to 4) severely repress DNA binding with Alpha2 and prevent much of the A1-Alpha-mediated repression (YGD, 2001). Mutations in the intervening sequence (IVS) of MATA1 has consequences for normal function and sporulation (YGD, 2001).