dsRNA made from templates generated with primers directed against this gene tested in RNAi screen for effects on Kc167 and S2R⁺ cell morphology.

The tub and pll proteins have different biochemical activities but are activated by the same mechanism in the dl nuclear localisation cascade. Membrane association and oligomerization are required for full activation of tub and pll.

tub is required for muscle development in the embryo.

Targeting of either tub or pll product to the plasma membrane by myristylation is sufficient to activate the signal transduction pathway that leads to translocation of the dl product. Activated Tl induces a localized recruitment of tub and pll proteins to the plasma membrane.

Yeast two hybrid assay demonstrates both tub and pll interact with dl. Interactions have also been confirmed in an in vitro binding assay. C terminus of tub is essential for the full activity of the protein.

tub, pll, cact and dl form a complex essential for signal transduction.

The embryonic regulatory pathway, comprising the gene products between spz and cact (Tl, tub and pll) but not the genes acting upstream or downstream (ea and dl), is involved in the induction of the Drs gene in adults. Mutations that affect the synthesis of antimicrobial peptides dramatically lower the resistance of flies to infection.

Interaction of the pll kinase with the membrane associated tub protein is required for transduction of the dorsoventral signal in embryos. The interaction of the pll protein with the tub protein is mediated by the putative regulatory domain of pll and not by the protein kinase catalytic domain. pll can function in signal transduction in the absence of tub and cannot act upstream of tub in the signaling pathway.

The tub protein can function in a novel way to enhance dl activity. In the absence of dl or when dl is cytoplasmic, tub is only found in the cytoplasm of transfected cells. When dl is localised to the nucleus, so is tub. tub can then function to enhance reporter gene expression, by cooperation with dl or as a Scer\GAL4-tub fusion protein. tub is capable of acting as both a chaperon or escort for dl as it moves to the nucleus and then as a transcriptional coactivator. The intracytoplasmic domain of Tl is sufficient for activating the signalling pathway that leads to dl-tub nuclear translocation in Schneider cells.

Deletions in the 3' UTR yield weakly ventralised embryos upon injection into tub and 107.1 mutant backgrounds. The deletions result in greater tub activity than in wild type embryos so the deletions may have hit regions of the transcript required to maintain low levels of tub.

Signal-dependent dl phosphorylation is modulated by three intracellular proteins, pll, tub and cact.

tub acts upstream of pll in the dorsoventral signal transduction pathway. The two-hybrid yeast interaction system demonstrates direct interaction of pll (bait) with tub (prey) to activate a reporter gene, Ecol\lacZ.

tub acts downstream of Tl indicating that the gene product is part of the machinery that transmits the signal from the Tl receptor to promote nuclear localisation of the dl gene product. tub is not essential for viability but lack of tub gene product decreases the chances of survival to adult stages. Lowering the dosage of pll strongly enhanced the phenotypes of all weak tub alleles. Double mutants of tub and pll show higher zygotic lethality than either single mutant.

The tub protein plays an essential role in the signal transduction pathway that establishes dorso-ventral polarity. Analysis of mutant alleles, interspecific sequence comparisons and RNA injection experiments with deleted tub genes indicate that the two halves of the tub proteins have functionally distinct roles in signal transduction.

Double mutant combinations of tub with ea alleles demonstrate that spatial regulation of ea activity by localized zymogen activation is a key initial event in defining the polarity of the dorsal-ventral embryonic pattern.

Genetic and molecular characterization of tub suggests that tub represents a class of protein active in signal transduction at two stages of development.

Mutations in maternal dorsal class gene tub do not interact with RpII140^wimp.

Analysis of mosaic females indicates that Ser, ea, snk and tub are expressed in the germline during oogenesis.