Growth, Differentiation and Sexuality

The cross of a mutant strain with an a mating partner
containing a wild-type ATPase encoding gene
gave abundant perithecia, which never developed
beaks, nor produced ascospores, mature or otherwise.
This ascus dominant phenotype suggests that
functional genes in both sexual partners may be
needed for the completion of the sexual cycle. Further
analyses of this gene and of the most conserved
companions of the mating-type genes should provide
interesting insights in the sexual cycle.
C. Main Features of Mating-Type Genes
and Proteins
1. MAT1-1-1
MAT1-1-1 proteins are characterized by the
presence of an α1 domain showing similarity to
the α1 transcription factor of S. cerevisiae and
to the Pc polypeptide from S. pombe (Fig. 15.4).
Although the role of the α1 proteinasaDNAbinding
protein has been substantiated, it has
not been placed in any of the large families of
sequence-specific DNA-binding proteins, such as
Fig. 15.4. Amino-acid alignment of the α1 box of deduced
MAT1-1-1 proteins of Euascomycetes with the MATα1
protein of S. cerevisiae. C. heterostrophus (CAA48465),
C. luttrellii (AAD33439), C. homomorphus (AAD33441),
C. kusanoi (AAD33443), A. alternata (BAA75907), C.
cymbopogonis (AAD33445), D. rabiei (Barve et al. 2003), P.
nodorum (AAO31740), N. crassa (AAC37478), S. macrospora
(CAA71623), P. anserina (CAA45519), C. globosum (Broad
Mating Types in Euascomycetes 307
homeodomain, zinc finger, or helix-loop-helix.
Surprisingly, the Pc polypeptide contains a HMG
domain that overlaps the region of similarity with
the α1 domain, suggesting a close relationship
between these two DNA-binding domains (Lu
and Turgeon, unpublished data). Both α1 and
Pc cooperate with additional regulatory proteins
for the control of mating and the expression of
cell type-specific genes. The α1 transcription
factor forms a complex with STE12 and MCM1
to activate the α haploid-specific genes in S.
cerevisiae (reviewed in Johnson 1995). Yuan et al.
(1993) have proposed that the region, located
between residues 90 and 111 of α1, interacts with
MCM1, but no experimental evidence supports
this interpretation. The Pc polypeptide interacts
physically with Map1, a protein belonging to the
MADS box family, which also includes MCM1
(Yabana and Yamamoto 1996). These data suggest
that Euascomycete homologs of MCM1/Map1
may cooperate with MAT1-1-1 to control the
expression of cell type-specific genes required for
fertilization. This hypothesis is supported by the
recent finding that the MCM1 protein is capable of
Institute), P. brassicae (CAA06844), R. secalis (CAD71141),
G. moniliformis/fujikuroi /(AAC71055), F. oxysporum
(BAA75910), G. zeae (AAG42809), P. tenuipes (BAC67541),
E. nidulans (AAQ01665), M. grisea (BAC65087), M.
graminicola (AAL30838), C. parasitica (AAK83346), S.
cerevisiae α1(NP_009969), S. pombe Pc (P10841). Fraction
ofsequencesthatmustagreeforshading:0.8