Plant Molecular Biology 39: 647–656, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
GRAB proteins, novel members of the NAC domain family, isolated by
their interaction with a geminivirus protein
es P. Sanz-Burgos
, Huishan Guo
, Juan Antonio Garc
Centro de Biolog
ia Molecular ‘Severo Ochoa’ (CSIC-UAM), Universidad Aut´onoma, Cantoblanco, 28049
28049 Madrid, Spain
Received 8 July 1998; accepted in revised form 7 October 1998
Key words: geminivirus, DNA replication, plant growth, senescence, NAC domain
Geminivirusesencode a few proteinsand depend on cellular factors to completetheir replicativecycle. As a way to
understand geminivirus-hostinteractions, we have searched for cellular proteins which interact with viral proteins.
By using the yeast two-hybrid technology and the wheat dwarf geminivirus (WDV) RepA protein as a bait, we
have isolated a family of proteins which we termed GRAB (for Geminivirus Rep A-binding). We report here the
molecular characterization of two members, GRAB1 and GRAB2. We have found that the 37 C-terminal amino
acids of RepA are required for interaction with GRAB proteins. This region contains residues conserved in an
equivalent regionof the RepA proteins encoded by other viruses of the WDV subgroup. The N-terminal domain of
GRAB proteins is necessary and sufﬁcient to interact with WDV RepA. GRAB proteins contain an unique acidic
C-terminal domain while their N-terminal domain, of ca. 170 amino acids, are highly conserved in all of them.
Interestingly, this conserved N-terminal domain of GRAB proteins exhibits a signiﬁcant amino acid homology to
the NAC domain present in proteins involved in plant development and senescence. GRAB1 and GRAB2 mRNAs
are present in cultured cells and roots but are barely detectable in leaves. GRAB expression inhibits WDV DNA
replication in cultured wheat cells. Our studies highlight the importance that the pathway(s) mediated by GRAB
proteins, as well as by other NAC domain-containing proteins, might have on geminivirus DNA replication in
connection to plant growth, development and senescence pathways.
Cellular processes regulating proliferation, growth
and differentiation are frequently interfered with dur-
ing viral infections by a mechanism involving the
interaction of viral proteins with cellular factors. The
molecular characterization of such interactions have
signiﬁcantly increased our present knowledge of ba-
sic cellular pathways. This is particularly evident for
viruses with small genomes, as it is the case of animal
DNA tumor viruses such as SV40  or human pa-
The nucleotide sequence data reported will appear in the
EMBL, GenBank and DDBJ Nucleotide Sequence Databases un-
der the accession numbers AJ010829 (GRAB1) and AJ010830
pilloma viruses , whose replicative cycle largely
depends on cellular functions.
The situation may be analogous in the case of
Geminiviridae, a unique family of plant DNA viruses
whosegenomeconsists ofone or two2.6–3.0kb circu-
lar single-stranded DNA molecules, depending on the
genus (reviewed in [5, 20]). Wheat dwarf geminivirus
(WDV), a member of the genus Mastrevirus, has one
of the smallest genomes (2750 nucleotides) and repli-
cates its DNA in the nucleus of the infected cells.
Because of the lack of replicative enzymesencoded by
the viral genome, it likely requires S-phase functions.
Consistent with this is the accumulation of replicative
intermediates in S-phase nuclei . Geminiviruses