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Mol. Cell. Biol., Jan 1998, 221-232, Vol 18, No. 1
AR Yee and JW Kronstad
The b mating-type locus of the fungal plant pathogen Ustilago maydis
encodes two multiallelic gene products, bE and bW, that control the
formation and maintenance of the infectious cell type. Dimerization via the
N-terminal regions of bE and bW proteins encoded by alleles of different
specificities establishes a homeodomain-containing transcription factor.
The bE and bW products encoded by alleles of like specificities fail to
dimerize. We constructed sets of chimeric alleles for the bE1 and bE2 genes
and for the bW1 and bW2 genes to identify sequences that control
specificity. The mating behavior of strains carrying chimeric alleles
identified three classes of specificity: b2 (class I), specificity
different from either parental type (class II), and b1 (class III). Crosses
between strains carrying bE and bW chimeric alleles identified two short
blocks of amino acids that influence specificity and that are located in
the N-terminal variable regions of the b proteins. Comparisons of pairs of
chimeric alleles encoding polypeptides differing in specificity and
differing at single amino acid positions identified 16 codon positions that
influence the interaction between bE and bW. Fifteen of these positions lie
within the blocks of amino acids identified by crosses between the strains
carrying chimeric alleles. Overall, this work provides insight into the
organization of the regions that control recognition.
Copyright © 1998, American Society for Microbiology
Dual sets of chimeric alleles identify specificity sequences for the bE and bW mating and pathogenicity genes of Ustilago maydis
Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
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