Deletion mutagenesis was used to identify sequences required for dimer
ization and enzymatic activity of the intracellular domain of the memb
rane guanylyl cyclase, GC-A. The intracellular domain of GC-A contains
a protein kinase-like domain near its amino terminus, a guanylyl cycl
ase catalytic domain near its carboxyl terminus, and, between these do
mains, a region of unknown function predicted to form an amphipathic a
lpha-helix. Gel filtration analysis of deletion mutants of the GC-A in
tracellular domain suggested that a 43 amino acid sequence within the
interdomain region was both necessary and sufficient for dimerization
and was required for guanylyl cyclase catalytic activity. The ability
of this sequence to mediate protein dimerization was confirmed in the
yeast two-hybrid system, in which its fusion to the lexA DNA-binding d
omain and to the VP16 transcriptional activation domain led to their d
imerization and consequent activation of a lexA-HIS3 gene. Thus, we ha
ve identified sequences responsible for dimerization of the intracellu
lar domain of a guanylyl cyclase and shown that they are required for
enzyme activity. Modulation of their interaction may be important in g
uanylyl cyclase activation.