Frequently, crop plants do not take up adequate amounts of iron from the soil, leading to chlorosis, poor yield and decreased nutritional quality. Extremely limited soil bioavailability of iron has led plants to evolve two distinct uptake strategies: chelation, which is used by the world's principal grain crops; and reduction, which is used by other plant groups. The chelation strategy involves extrusion of low-molecular-mass secondary amino acids (mugineic acids) known as 'phytosiderophores' which chelate sparingly soluble iron. The Fe(III)-phytosiderophore complex is then taken up by an unknown transporter at the root surface. The maize yellow stripe1 (ys1) mutant is deficient in Fe(III)-phytosiderophore uptake, therefore YS1 has been suggested to be the Fe(III)-phytosiderophore transporter. Here we show that ys1 is a membrane protein that mediates iron uptake. Expression of YS1 in a yeast iron uptake mutant restores growth specifically on Fe(III)-phytosiderophore media. Under iron-deficient conditions, ys1 messenger RNA levels increase in both roots and shoots. Cloning of ys1 is an important step in understanding iron uptake in grasses, and has implications for mechanisms controlling iron homeostasis in all plants.

The protein factor U2 snRNP Auxiliary Factor (U2AF) 65 is an essential component required for splicing and involved in the coupling of splicing and 3 0 end processing of vertebrate pre-mRNAs. Here we have addressed the mechanisms by which U2AF 65 stimulates pre-mRNA 3 0 end processing. We identify an arginine/serine-rich region of U2AF 65 that mediates an interaction with an RS-like alternating charge domain of the 59 kDa subunit of the human cleavage factor I (CF I m ), an essential 3 0 processing factor that functions at an early step in the recognition of the 3 0 end processing signal. Tethered functional analysis shows that the U2AF 65/CF I m 59 interaction stimulates in vitro 3 0 end cleavage and polyadenylation. These results therefore uncover a direct role of the U2AF 65/CF I m 59 interaction in the functional coordination of splicing and 3 0 end processing.