The titan ( ttn ) mutants of Arabidopsis exhibit dramatic alterations in mitosis and cell cycle control during seed development. Endosperm development in these mutants is characterized by the formation of giant polyploid nuclei with enlarged nucleoli. Embryo development is accompanied by significant cell enlargement in some mutants ( ttn1 and ttn5 ) but not others ( ttn2 and ttn3). We describe here the molecular cloning of TTN5 using a T-DNA-tagged allele. A second allele with a similar phenotype contains a nonsense mutation in the same coding region. The predicted protein is related to ADP ribosylation factors (ARFs), members of the RAS family of small GTP binding proteins that regulate various cellular functions in eukaryotes. TTN5 is most closely related in sequence to the ARL2 class of ARF-like proteins isolated from humans, rats, and mice. Although the cellular functions of ARL proteins remain unclear, the ttn5 phenotype is consistent with the known roles of ARFs in the regulation of intracellular vesicle transport. INTRODUCTIONEmbryo-defective mutants of Arabidopsis have been used for many years to identify genes with essential functions during plant embryogenesis (Goldberg et al., 1994;Jurgens et al., 1994;Meinke, 1995). Recent advances in gene isolation have made it possible to recover increasing numbers of these genes and study their role in plant growth and development (Li and Thomas, 1998;Lotan et al., 1998;Patton et al., 1998;Uwer et al., 1998;Albert et al., 1999). Development of the female gametophyte and early endosperm in Arabidopsis has also been subjected to extensive genetic analysis (Drews et al., 1998;Berger, 1999). Particular attention has been given to mutants with defects in gene imprinting and mutants in which endosperm development begins in the absence of fertilization (reviewed in Preuss, 1999). Molecular cloning of the medea ( med ) and fertilization-independent endosperm and seed ( fie and fis , respectively) genes (Grossniklaus et al., 1998;Kiyosue et al., 1999;Luo et al., 1999;Ohad et al., 1999) has renewed interest in the biochemical signals associated with fertilization and the coordinated development of the gametophyte, embryo, and endosperm tissue in plants.The titan ( ttn ) mutants of Arabidopsis represent another interesting class of mutants with defects in embryo and endosperm development (Liu and Meinke, 1998). The most striking feature of these mutants is the formation of giant endosperm nuclei and nucleoli during early stages of seed development. Embryo development is arrested shortly after fertilization in most ttn mutants and in some cases is accompanied by dramatic cell enlargement. Three nonallelic ttn mutants ( ttn1 , ttn2 , and ttn3 ) with related but distinct phenotypes were first described by Liu and Meinke (1998). The ttn1 phenotype includes extraordinary enlargement of nuclei in the embryo and endosperm, similar enlargement of cells in the arrested embryo, and a disruption of endosperm nuclear migration to the chalazal end of the seed. Defects in ttn2 are limited...

The titan (ttn) mutants of Arabidopsis exhibit dramatic alterations in mitosis and cell cycle control during seed development. Endosperm development in these mutants is characterized by the formation of giant polyploid nuclei with enlarged nucleoli. Embryo development is accompanied by significant cell enlargement in some mutants (ttn1 and ttn5) but not others (ttn2 and ttn3). We describe here the molecular cloning of TTN5 using a T-DNA-tagged allele. A second allele with a similar phenotype contains a nonsense mutation in the same coding region. The predicted protein is related to ADP ribosylation factors (ARFs), members of the RAS family of small GTP binding proteins that regulate various cellular functions in eukaryotes. TTN5 is most closely related in sequence to the ARL2 class of ARF-like proteins isolated from humans, rats, and mice. Although the cellular functions of ARL proteins remain unclear, the ttn5 phenotype is consistent with the known roles of ARFs in the regulation of intracellular vesicle transport.

A test procedure for thermal life testing of polyimide wrapped medium voltage machines has been developed and initial testing has occurred. Polyimide wrapped medium voltage motors, such as those tested by this new procedure, are primarily used in electric submersible pump (ESP) systems. Current thermal life testing standards do not adequately support these ESP machines. The reason for the gap in the standards as currently constituted is the unique design constraints that are imposed on ESP machines by their oilfield applications.ESP motors are used in deep, downhole applications that require wide ranges of horsepower and a supply voltage between 2kV and 7kV. These motors must fit into an oil well casing that imposes a motor frame with an outside diameter between 3 and 9 inches. These design requirements significantly restrict the design of the insulation system. In most cases machine designs are polyimide wrapped (most areas of the machine have less than 10 mils of insulation) polyimide-based systems. The new test procedures are based on existing standards but take into consideration the unique design and the unique application of ESP motors. This paper discusses the distinctive aspects of the machine's application and design, outlines the new testing procedure and reviews initial test results. Further, this paper discusses how this testing procedure fits into the landscape of insulation life testing standards.