J. Mcelver et al., The TITAN5 gene of arabidopsis encodes a protein related to the ADP ribosylation factor family of GTP binding proteins, PL CELL, 12(8), 2000, pp. 1379-1392
The titan (ttn) mutants of Arabidopsis exhibit dramatic alterations in mito
sis and cell cycle control during seed development. Endosperm development i
n these mutants is characterized by the formation of giant polyploid nuclei
with enlarged nucleoli. Embryo development is accompanied by significant c
ell enlargement in some mutants (ttn1 and ttn5) but not others (ttn2 and tt
n3). We describe here the molecular cloning of TTN5 using a T-DNA-tagged al
lele. A second allele with a similar phenotype contains a nonsense mutation
in the same coding region. The predicted protein is related to ADP ribosyl
ation factors (ARFs), members of the RAS family of small GTP binding protei
ns that regulate various cellular functions in eukaryotes. TTN5 is most clo
sely related in sequence to the ARL2 class of ARF-like proteins isolated fr
om humans, rats, and mice. Although the cellular functions of ARL proteins
remain unclear, the ttn5 phenotype is consistent with the known roles of AR
Fs in the regulation of intracellular vesicle transport.