THE PLANT CELL, Vol 7, Issue 6 773-783, Copyright © 1995 by American Society of Plant Biologists
An N-Terminal Dimerization Domain Permits Homeodomain Proteins To Choose Compatible Partners and Initiate Sexual Development in the Mushroom Coprinus cinereus
A. H. Banham, R. N. Asante-Owusu, B. Gottgens, SAJ. Thompson, C. S. Kingsnorth, EJC. Mellor and L. A. Casselton
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, United Kingdom
The A mating-type locus of the mushroom Coprinus cinereus contains three or
more paralogous pairs of genes encoding two families of homeodomain
proteins (HD1 and HD2). A successful mating brings together different
allelic forms of at least one gene, and this is sufficient to trigger
initial steps in sexual development. Previous studies have suggested that
development is regulated by heterodimerization between HD1 and HD2
proteins. In this report, we describe 5[prime] gene deletions and 5[prime]
end exchanges showing that the N-terminal regions of the proteins are
essential for choosing a compatible partner but not for regulating gene
transcription. Using an in vitro glutathione S-transferase association
assay, we demonstrated heterodimerization between HD1 and HD2 proteins and
found that heterodimerization only occurs between compatible protein
combinations. The N-terminal regions of the proteins were sufficient to
mediate dimerization, and N-terminal swaps resulted in a predicted change
in dimerization specificity. By analyzing the N-terminal amino acid
sequences of HD1 proteins, we identified two potential coiled-coil motifs
whose relative positions vary in paralogous proteins but are both required
for in vivo function.
