The b alleles of U. maydis, whose combinations program pathogenic development, code for polypeptides containing a homeodomain-related motif.
U. maydis is a fungal pathogen of corn with two forms: one is yeast-like and nonpathogenic; the other is filamentous and pathogenic. The b locus, with 25 different alleles, regulates this dimorphism: any combination of two different alleles triggers pathogenic development, whereas the presence of identical alleles results in the yeast-like form. We have cloned four b alleles (b1, b2, b3, and b4) and show that the b locus contains a single open reading frame (ORF) of 410 amino acids with a variable N-terminal region and a highly conserved C-terminal region (60% and 93% identity, respectively). Mutational analysis confirms that this ORF is responsible for b activity. The b polypeptides appear to be DNA binding proteins because they contain a motif related to the homeodomain in their constant region. We propose that combinatorial interactions between b polypeptides generate regulatory proteins that determine the developmental program of the fungus.
Schulz
B
B
Institut für Genbiologische Forschung Berlin GmbH, Federal Republic of Germany.
Banuett
F
F
Dahl
M
M
Schlesinger
R
R
Schäfer
W
W
Martin
T
T
Herskowitz
I
I
Kahmann
R
R
D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D001487:Basidiomycota / Q000235:genetics*; D015139:Blotting, Southern; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000235:genetics / Q000302:isolation & purification; D005656:Fungal Proteins / Q000235:genetics; D005800:Genes, Fungal; D005801:Genes, Homeobox; D006720:Homozygote; D008969:Molecular Sequence Data; D010957:Plasmids; D012689:Sequence Homology, Nucleic Acid; D014588:Ustilago / Q000235:genetics* / Q000472:pathogenicity; D003313:Zea mays / Q000254:growth & development
D004271:DNA, Fungal; D005656:Fungal Proteins