Plant Molecular Biology 33: 537–544, 1997.
1997 Kluwer Academic Publishers. Printed in Belgium.
Two genes for the high mobility group protein HMG-Y are present in the
genome of Canavalia gladiata D.C.
and Takao Minamikawa
Department of Biology, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo, 192-03 Japan;
address: Bionic Design Group, National Institute for Advanced Interdisciplinary Research, Tsukuba, Ibaraki, 305
author for correspondence)
Received 6 August 1996; accepted in revised form 4 November 1996
Key words: A/T hook, A/T-rich sequence, Canavalia gladiata. GRP motif, high-mobility-group (HMG) protein,
seed storage protein
Two cDNAs encoding high-mobility-group (HMG) proteins that correspond to animal HMG-Y proteins were
isolated from maturing seeds of Canavalia gladiata D.C. The deduced amino acid sequences of these cDNAs
showed similarity to other plant HMG-I/Y proteins reported to date. The mRNAs for the HMG-Y proteins were
detected in leaves, stems, roots, pods and seeds of C. gladiata. The level of the mRNA was high in the maturing
seeds of 30 days after ﬂowering and 2-day germinated seeds. Two genomic clones were isolated from DNA of
C. gladiata and both were shown to represent single-copy genes consisting of two exons and one intron. This is the
ﬁrst report of the genomic sequences for HMG-I/Y protein in plants.
We have been interested in A/T-rich sequences which
are contained in the 5
-upstream regions of the genes
encoding concanavalin A (Con A) and canavalin, two
major seed storage proteins of Canavalia gladiata D.C.
. The expression of the genes encoding Con A
and canavalin is restricted to seeds and the genes are
most active at about 40 days after ﬂowering (DAF)
, middle stage of maturation. To elucidate the roles
of A/T-rich sequences in the gene expression, HMG
proteins were focused as nuclear proteins that interact
with A/T-rich sequences in the 5
-upstream regions of
the Con A and canavalin genes.
The plant HMG proteins, as well as the corres-
pondingmammalianproteins, can be divided into three
groups:HMG-1/2, HMG-14/17 and HMG-I/Y.The
HMG-1/2 proteins contain HMG-box DNA-binding
domains. The cDNA clone of the plant HMG-1/2 pro-
The nucleotide sequence data reported will appear in the
EMBL, GenBank and DDBJ Nucleotide Sequence Databases under
the accession numbers D83070 (pCY1), D83071 (pCY2), D86594
(CgHMGY1) and D86595 (CgHMGY2).
tein was ﬁrst isolated from maize  and found to con-
tain only one HMG-box in contrast to animal HMG-1/2
proteins which have two. The HMG-14/17 proteins
have nucleosome-binding characteristics . There
is little work reported on plant HMG-14/17 proteins.
The HMG-I/Y proteins bind preferentially to A/T-rich
stretches of double-stranded DNA . The human
HMG-I and HMG-Y proteins are products of altern-
ative splicing of a common transcript and the former
contain an 11 amino acid-long hydrophobic insertion
. In plants, the cDNA clones of HMG-I/Y were
isolated from soybean , rice  and oat . Soy-
bean and rice HMG-I/Y proteins contain four repeats
of the A/T-hook DNA-binding motif , whereas the
human HMG-I/Y contains three repeats . Interest-
ingly, the tobacco HMG-I-like protein, ATBP-1, has
been reported to contain seven repeats of the A/T-hook
motif . The plant HMG-I/Y proteins are about
twice as large as the mammalian HMG-I/Y proteins
of around 10 kDa .
HMG-I/Y proteins are the most likely candidate
for the nuclear protein that interacts with A/T-rich
sequences in the 5
-upstream regions of the Con A