SUMMARY PARAGRAPH for HMRA1
a1 is one of two genes encoded by the a mating type cassette in S. cerevisiae (5). The mating type of S. cerevisiae is determined by the genetic composition of the MAT locus (7, 5, 6). Haploids of the a mating type express the genes a1 and a2 from the MAT locus while haploids of the alpha mating type express alpha1 and alpha2 from MAT (7, 5, 6). Some of the cells within a given colony are capable of switching mating type by changing the genetic composition of the MAT locus (8); more information on mating type switching can be found in the summary paragraph for MAT and references cited therein. Diploid cells are normally heterozygous (a/alpha) at the MAT locus (7, 5, 6).
a1 encodes a homeodomain protein involved in transcriptional regulation of mating-type-specific genes (1, 3, 5, 6). The a1 protein is produced in haploid MATa cells, but does not play any known role in a-specific gene expression, and is rapidly degraded (5, 9). In a/alpha diploid cells, a1p interacts with another homeodomain protein, alpha2p, to bind DNA as a heterodimer to repress transcription of haploid-specific genes (1, 5, 3, 6, 4, 2, 10). The interaction between a1p and alpha2p stabilizes both proteins, and alters their DNA binding specificities (1, 4, 9, 11).
Note: The maps and sequences within SGD reflect the fact that a MATalpha strain was used in the systematic sequencing project. Accordingly, there are two copies of the alpha1 and alpha2 genes; one pair (MATalpha1/YCR040W and MATalpha2/YCR039C) corresponds to the MAT locus, and the other (HMLalpha1/YCL066W and HMLalpha2/YCL067C) to the HML locus. There are ORFs assigned to the copies of a1 and a2 found at HMR (HMRa1/YCR097W) and (HMRa2/YCR096C); locus entries are included for MATa1 and MATa2 but they do not have ORFs associated with them. There are GenBank sequences available from all of the locus pages describing a1, a2, alpha1, and alpha2; the Genbank accession for the MATa cassette is V01313.
Last updated: 2000-08-15