Reference "Auxin-binding protein--antibodies and genes"

Reference ID

7601

Title

Auxin-binding protein--antibodies and genes

Source

Symposia of the Society for Experimental Biology, 1991, vol. 45, pp. 129-148

Authors (5)

Lazarus-C-M	Napier-R-M
Yu-L-X	Lynas-C
Venis-M-A

Abstract

Of several auxin-binding systems that have been characterised the auxin-binding
protein (ABP) of maize coleoptile membranes is the best candidate for a true
auxin receptor. ABP, which exists as a homodimer of 22 x 10(3) M(r) glycosylated
subunits, has been purified, and monoclonal and polyclonal antibodies raised
against it. Electrophysiological studies with antibodies indicated the presence
of a functional population of auxin receptors on the exterior face of the
plasmalemma; electrophysiological experiments with impermeant auxin analogues
now reinforce this conclusion. An epitope mapping kit has been used to identify
the major epitopes recognised by antibody preparations. Three major epitopes,
bracketing the glycosylation site, have been identified in the polyclonal serum.
They are also represented in antisera produced in other laboratories and are
conserved in ABP prepared from other plants. One monoclonal antibody recognises
an epitope close to the amino terminus of ABP and two others recognise the
carboxy terminus. The latter antibodies have been used in a sandwich ELISA to
demonstrate that auxin binding induces a conformational change in ABP. Maize ABP
is encoded by a small gene family and cDNA and genomic clones have been
isolated. With a single exception, predicted amino acid sequences indicate
remarkably little heterogeneity. The exceptional cDNA sequence predicts 87%
amino acid homology with the major class of proteins. Four introns are apparent
in the sequence of a complete ABP gene; their sequences are very highly
conserved in an incompletely-cloned second gene lacking the first exon. The
major difference between the two genes lies in the length of the first intron,
which has been estimated to exceed 5.2 kb in the incomplete gene. The site of
initiation of transcription has not been unambiguously identified in the
complete gene, and some evidence suggests that there may be an additional
intron. Homology to maize ABP cDNA has been detected in the genomes of
Arabidopsis, spinach and strawberry but not in that of tobacco. A sequence
located within the 3'-half of the maize cDNA is highly repeated in the
strawberry genome, from which clones with homology to both halves of the maize
cDNA (i.e. putative ABP genes) have been isolated.