U. Kues et al., 2 CLASSES OF HOMEODOMAIN PROTEINS SPECIFY THE MULTIPLE-A MATING TYPESOF THE MUSHROOM COPRINUS-CINEREUS, The Plant cell, 6(10), 1994, pp. 1467-1475
The A mating type locus of the mushroom Coprinus cinereus regulates es
sential steps in sexual development. The locus is complex and contains
several functionally redundant, multiallelic genes that encode putati
ve transcription factors. Here, we compare four genes from an A locus
designated A42. Overall, the DNA sequences are very different (similar
to 50% homology), but two classes of genes can be distinguished on th
e basis of a conserved homeodomain motif in their predicted proteins (
HD1 and HD2). Development is postulated to be triggered by an HD1 and
an HD2 gene from different A loci. Thus, proteins encoded by genes of
the same locus must be distinguished from those encoded by another loc
us. Individual proteins of both classes recognize each other using the
region N-terminal to the homeodomain. These N-terminal specificity re
gions (COP1 and COP2) are predicted to be helical and are potential di
merization interfaces. The amino acid composition of the C-terminal re
gions of HD1 proteins suggests a role in activation, and gene truncati
ons indicate that this region is essential for function in vivo. A cor
responding C-terminal region in HD2 proteins can be dispensed with in
vivo. We will discuss these predicted structural features of the C. ci
nereus A proteins, their proposed interactions following a compatible
cell fusion, and their similarities to the a1 and alpha 2 mating type
proteins of the yeast Saccharomyces cerevisiae.