A linker region of the yeast zinc cluster protein leu3p specifies binding to everted repeat DNA

Yeast zinc cluster proteins form a major class of yeast transcriptional regulators. They usually bind as homodimers to target DNA sequences, with each monomer recognizing a CGG triplet. Orientation and spacing between the CGG triplet specifies the recognition sequence for a given zinc cluster protein. For instance, Gal4p binds to inverted CGG triplets spaced by 11 base pairs whereas Ppr1p recognizes a similar motif but with a spacing of 6 base pairs. Hap1p, another member of this family, binds to a direct repeat consisting of two CGG triplets. Other members of this family, such as Leu3p, also recognize CGG triplets but when oriented in opposite directions, an everted repeat. This implies that the two zinc clusters of Leu3p bound to an everted repeat must be oriented in opposite directions to those of Gal4p or Ppr1p bound to inverted repeats. In order to map the domain responsible for proper orientation of the zinc clusters of Leu3p, we constructed chimeric proteins between Leu3p and Ppr1p and tested their binding to a Leu3p and a Ppr1p site. Our results show that the linker region, which bridges the zinc cluster to the dimerization domain, specifies binding of Leu3p to an everted repeat. We propose that the Leu3p linker projects the two zinc clusters of a Leu3p homodimer in opposite directions allowing binding to everted repeats.