Cloning of cutinase transcription factor 1, a transactivating protein containing Cys6Zn2 binuclear cluster DNA-binding motif

Abstract

Hydroxy fatty acids from plant cutin were shown previously to induce the expression of the cutinase gene via a palindromic sequence located at -159 base pairs of the cutinase gene in Fusarium solani f. sp. pisi (Nectria hematococca mating type VI). Of the two overlapping palindromes in this sequence, palindrome 2 was found to be essential for the inducibility of cutinase by hydroxy fatty acids. Screening of a phage expression library with the concatenated palindrome 2 as probe detected a distinct cDNA clone encoding a polypeptide designated cutinase transcription factor 1α (CTF1α) with a calculated molecular weight of 101,109. This protein contains a Cys6Zn2 binuclear cluster motif sharing homology to the Cys6Zn2 binuclear cluster DNA-binding domains of transcription factors from Saccharomyces cerevisiae, S. carlsbergensis, Kluyveromyces lactis, Neurospora crassa, Aspergillus nidulans, and A. flavus. CTF1α, expressed in Escherichia coli, showed specific binding to the palindrome 2 DNA fragment but not to palindrome 1 or mutant palindrome 2 DNA fragments, suggesting specific binding of CTF1a to palindrome 2. When CTF1α was expressed as a fusion protein with the nuclear localization sequence of SV40 in yeast, it transactivated the native cutinase promoter fused to the chloramphenicol acetyl transferase (cat) gene. Mutation of palindrome 2 but not palindrome 1 abolished this transactivation. Thus, CTF1α positively acts in vivo by binding selectively to palindrome 2 of the cutinase gene promoter.