Plant Molecular Biology 36: 451–461, 1998.
1998 Kluwer Academic Publishers. Printed in Belgium.
Isolation and characterization of two cyclin-like cDNAs from Arabidopsis
Irene S. Day & A.S.N. Reddy
Department of Biology and Program in Cell and Molecular Biology, Colorado State University, Fort Collins,
CO 80523, USA (
author for correspondence)
Received 19 March 1997; accepted in revised form 6 October 1997
Key words: Arabidopsis, cell cycle, cell division, cyclins, cyclin-dependentkinases
Cyclins are key regulators of a family of protein kinases called cyclin-dependent kinases (Cdks). Speciﬁc cyclins
interact with speciﬁc Cdks to regulate the different transition points in the cell cycle. Six mitotic-like cyclins
have previously been reported in Arabidopsis thaliana. Using polymerase chain reaction ampliﬁed cyclin-box
sequences as probes, two new cyclin cDNAs are isolated from Arabidopsis. The deduced amino acid sequences
of the isolated cDNAs (Arath;CycB1;3 and Arath;CycB1;4) show the highest sequence similarity with mitotic
cyclins. Arath;CycB1;3is mosthomologousto the plantCycB1groupcyclinsandcontainsa conservedmotif that is
typicalof this group. Arath;CycB1;4,while homologoustoArath;CycB1;2, has some features that makeit different
from other known mitotic-like cyclins. These data suggest the presence of several distinct cyclins of CycB1 group
in Arabidopsis. Analysis of expression of three members of CycB1 group (Arath;CycB1;2, Arath;CycB1;3 and
Arath;CycB1;4)in different tissues by reversetranscription-polymerasechainreaction usingprimerscorresponding
to unique regions of their cDNAs shows that they are differentially expressed in different tissues.
Cell division in eukaryotes is tightly regulated at key
points in the cell cycle. An interaction between two
(Cdks),has beenshowntobeinvolvedin theregulation
ofthesetransitions. Boththese proteinsarerepresented
in the genome as gene families. In animals, a large
family of Cdks has been identiﬁed [33, 35, 36, 52].
Similarly a family of cyclin genes has been identiﬁed
in both yeast [1, 6, 17, 26] and animals [22, 33, 35].
Speciﬁc cyclins interact with speciﬁc Cdks to regulate
the different transition points [31, 33, 52]. Proteins are
classiﬁed as members of the cyclin family on the basis
of sequence similarity limited to a central region (the
cyclin-box) of about 200 amino acids that are ﬂanked
by divergent N- and C-terminal regions . Cyclins
have been generally divided into two groups: mitotic
cyclins which are involved in the G2/M transition and
The nucleotide sequences data reported will appear in the
EMBL, GenBank, DDBJ Nucleotide Sequence Databases under the
accession numbers L27224 and L27225.
G1 cyclins involved at Start and the G1/S transition.
Mitotic cyclins have a motif called a destruction box
that has been implicated in their destruction through
the ubiquitin pathway [16, 26].
Cyclins were ﬁrst isolated in plants from carrots
and soybean in 1991 . Since then, 61 cyclins have
been identiﬁed in 14 species of plants representing
seven angiosperm families . All plant cyclins in
this report are referred to by the names suggested by
Renaudin et al. . Recently a cyclin has been isol-
ated from a fern, Adiantum capillus-veneris L. .
Many of the cyclins were isolated using probes gen-
erated by PCR ampliﬁcation of cyclin box sequences
[4, 5, 10, 21, 37, 41, 46, 50] oligonucleotide probes
based on the cyclin box [18, 19], or cyclin clones
[13, 45]. Because the cyclin box sequence in G1-
type cyclins shows very limited homology compared
to the homology between the mitotic-type cyclins, all
of the cyclins isolated using these methodswere of the
mitotic-type. However, they were not easily classiﬁed
as A orB type becausetheir cyclin-boxsequencescon-
tained conserved residues from both types. Phylogen-