Résumé
The site I 22 kDa auxin‐binding proteins from maize are encoded by a small gene family comprising at least five members. Here the cloning and molecular analysis of the
Zm‐ERabp1
,
Zm‐ERabp4
, and
Zm‐ERabp5
genes is presented. All three encode 22–23 kDa proteins displaying a transit peptide, a C‐terminal KDEL sequence, as well as glycosylation and auxin‐binding sites. The
Zm‐ERabp4
and
Zm‐ERabp5
genes are very similar. The
Zm‐ERabp1
gene encodes a related protein, but its promoter, leader and signal peptide are very different. Northern analysis using gene‐specific oligonucleotide probes indicates that
Zm‐ERabp4
is expressed in leaves and coleoptiles but weakly in roots, whereas
Zm‐ERabp5
expression is barely detectable in these tissues. RNA‐PCR indicated that all three genes are none the less expressed in many tissues. Primer‐extension analysis revealed an unusually long (320 bases)
Zm‐ERabp1
leader containing an 80 codon ORF which, if expressed, would encode a positively charged protein with some similarity to transcription factors. In a transient promoter—reporter gene expression system using maize leaf protoplasts the
Zm‐ERabp1
promoter is more active than the
Zm‐ERabp4
and
Zm‐ERabp5
promoters. Promoter deletion analysis of
Zm‐ERabp1
has identified a negative regulatory sequence in a region from −364 bp and −130 bp, deletion of which results in about twofold higher expression. This region contains both enhancer‐ and G‐box‐related sequences. Deletion of −129 bp to +64 bp, which contains the TATA box and transcription start, results in a large decrease in expression.