are present and highly conserved whereas the presence of various other proteins is yet to be explored. The
availability of these genes will help in studying the detailed regulation of various components involved
in the cell cycle.- Plant Cdks
The first evidence of a p34cdc2(cdc2) homologue in plants came from studies with antibodies to an inter-
nal peptide containing the highly conserved EGVPSTAIREISLLKE motif found only in Cdks, the car-
boxy-terminal 127 amino acids of the human cdc2 homologue or the whole Saccharomyces pombecdc2
protein [96]. A 34-kDa protein was detected by the antibodies in cell extracts from oats, Arabidopsis, and
algae. Phosphorylation of the 34-kDa protein identified in the green algae Chlamydomonaswas correlated
to the time of commitment to divide and dephosphorylation to the end of mitosis. In another study, mon-
oclonal antibodies to cdc2 were also used to identify the presence of a 34-kDa protein in 10 different plant
species [97]. In some species there was a polymorphism around 34 kDa. In protein extracts from mitoti-
cally nonsynchronous cell populations, this polymorphism has been attributed to distinct phosphorylation
states of the protein [97].
Since 1990, molecular cloning techniques have been utilized to isolate cdc2 homologues. Table 4
lists the isolated genes and some of their characteristics. Homologues have been identified in alfalfa
CELL CYCLE REGULATION IN PLANTS 235TABLE 4 Plant Cyclin-Dependent Kinases
Gene Phosphorylation sites
Plant name No. of aaa MWb PSTAIREc TYd Te Rescuef Reference
Alfalfa cdc2MsA 294 33,886 PSTAIRE GEGTYGV RTFTHEV cdc2 98
cdc2MsB 294 33,864 PSTAIRE GEGTYGV RTFTJEV cdc28 98
cdc2MsC 509 57,000 PITALRE GEGTYGM ANLTNRV NR 99
cdc2MsD 311 35,000 PPTALRE GEGTYGK KSYTHEI NR 99
cdc2MsE 414 g SPTAIRE g LSENGVV NR 99
cdc2MsF 316 36,000 PPTTLRE GEGTYGK KKYTHEI NR 99
Antirrhinum cdc2a NR NR PSTAIRE GEGTYGV RTFTHEV cdc2 100
cdc2b NR NR PSTAIRE GegAYGV RTFTHEY cdc2 100
cdc2c NR NR PPTALRE GEGTYGK KSYTHEI no 100
cdc2d NR NR PPTTLRE GEGTYGV RTFTHEV no 100
Arabidopsis cdc2a 294 34,008 PSTAIRE GEGTYGV RTFTHEV cdc28 101
cdc2 103
cdc2b 309 35,295 PPTALRE GEGTYGK KSYTHEI NR 102
cdc2c 644 72,300 PSTAIRE GQGTYSS NQLTSRV NR 104
Maize cdc2ZmA 294 33,812 PSTAIRE GEGTYGV RTFTHEV cdc28 105
cdc2ZmB ggPSTAIRE gg 105
Mothbean cdc2 294 33,961 PSTAIRE GEGTYGV RTFTHEI NR 106
N. spruce cdc2Pa 294 33,702 PSTAIRE GEGTYGV RTFTHEV NR 107
Pea cdkPs1 294 33,864 PSTAIRE GEGTYGV RTFTHEV cdc28 97
cdkPs2 294 33,900 PSTAIRE NR cdc28 21
cdkPs3 18 57,524 PITAIRE NR NR 21
Petunia cdc2Pet ggPSTAIRE gg 108
Rice cdc20s-1 294 34,049 PSTAIRE GEGTYGV RTFTHEV cdc28 109
cdc20s-2 292 33,671 PSTAIRE GEGTYGV RTFTHEV h 109
R2 424 47,582 NFTALRE GEGTYGV RNFTHQV h 110
Soybean cdc2-S5 294 33,940 PSTAIRE GEGTYGV RTFTHEV cdc28 111
cdc2-S6 294 33,950 PSTAIRE GEGTYGV RTFTHEV cdc28 111
Tobacco cdc2Nt1 294 33,900 PSTAIRE GEGTYGV RTFTHEV cdc28 112
Tomato cdkA1 294 33,700 PSTAIRE GEGTYGV RTFTHEV NR 113
cdkA2 294 33,700 PSTAIRE GEGTYGV RTFTHEV NR 113
aPredicted number of amino acids in derived polypeptide.
bPredicted molecular weight of derived polypeptide.
cComposition of “PSTAIRE” domain.
dT-14, Y-15 in p34cdc2.
eT-161 in p34cdc2.
fRescue of temperature-sensitive (ts) cdc28mutant of S. cerevisiaeor ts cdc2mutant of S. pombe.
gData unavailable due to truncated clone.
hFailed to rescue S. cerevisiae cdc28mutants.
NR, not reported.