The molecular basis for the transport of manganese across membranes in plant cells is poorly understood. We have found that IRT1, an Arabidopsis thaliana metal ion transporter, can complement a mutant Saccharomyces cerevisiae strain defective in high-affinity manganese uptake (smf1 delta). The IRT1 protein has previously been identified as an iron transporter. The current studies demonstrated that IRT1, when expressed in yeast, can transport manganese as well. This manganese uptake activity was inhibited by cadmium, iron(II) and zinc, suggesting that IRT1 can transport these metals. The IRT1 cDNA also complements a zinc uptake-deficient yeast mutant strain (zrt1zrt2), and IRT1-dependent zinc transport in yeast cells is inhibited by cadmium, copper, cobalt and iron(III). However, IRT1 did not complement a copper uptake-deficient yeast mutant (ctr1), implying that this transporter is not involved in the uptake of copper in plant cells. The expression of IRT1 is enhanced in A. thaliana plants grown under iron deficiency. Under these conditions, there were increased levels of root-associated manganese, zinc and cobalt, suggesting that, in addition to iron, IRT1 mediates uptake of these metals into plant cells. Taken together, these data indicate that the IRT1 protein is a broad-range metal ion transporter in plants.

Abstract. Capping protein nucleates the assembly of actin filaments and stabilizes actin filaments by binding to their barbed ends. We describe here a novel isoform of the/~ subunit of chicken capping protein, the/32 isoform, which arises by alternative splicing. The chicken/31 isoform and the t2 isoform are identical in their amino acid sequence except for a short region at the COOH terminus; this region of the/3 subunit has been implicated in binding actin. Human and mouse cDNAs of the fll and t2 isoforms also were isolated and among these vertebrates, the COOH-terminal region of each isoform is highly conserved. In contrast, comparison of the sequences of the vertebrate fl subunit COOH-termini to those of lower eukaryotes shows no similarities.The t2 isoform is the predominant isoform of nonmuscle tissues and the fll isoform, which was first characterized in studies of capping protein from chicken muscle, is the predominant isoform of muscle tissues, as shown by immunoblots probed with isoform-specific antibodies and by RNAse protection analysis of mRNAs. The/32 isoform also is a component of dynactin complex from brain, which contains the actin-related protein Arpl. Both/~-subunit isoforms are expressed in cardiac muscle but they have nonoverlapping subcellular distributions. The fll isoform is at Z-discs of myofibrils, and the ~2 isoform is enriched at intercalated discs; in cardiac myocytes grown in culture, the t2 isoform also is a component of cell-cell junctions and at sites where myofibrils contact the sarcolemma. The biochemical basis for the differential distribution of capping protein isoforms is likely due to interaction with specific proteins at Z-discs and cell-cell junctions, or to preferential association with different actin isoforms. Thus, vertebrates have developed isoforms of capping protein that associate with distinct actin-filament arrays. F UNI)AMeNTAt. processes of biological systems include generation of asymmetric shapes and movement. The actin cytoskeleton is an essential component of these processes, which are often dynamic and take on diverse forms in different cell types and tissues. Within a single cell, distinct populations of actin filaments can exist, some of which may be formed by a distinct actin isoform. The different actin filament arrays contain several different actinbinding proteins, which likely interact with actin to regulate its assembly. Many of the actin-binding proteins also are expressed as isoforms which may contribute to generate diversity in the organization of actin filaments in cells and tissues.Capping protein is a candidate for regulating actin filament assembly in vivo. In vitro, capping protein nucleates filament

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Craniofacial abnormalities are one of the most common birth defects in humans, but little is known about the human genes that control these important developmental processes. To identify relevant genes, we analyzed transcription profiles of human pharyngeal arch 1 (PA1), a conserved embryonic structure that develops into the palate and jaw. Using microdissected, normal human craniofacial structures, we constructed 12 SAGE (serial analysis of gene expression) libraries and sequenced 606 532 tags. We also performed Affymetrix microarray analysis on 25 craniofacial targets. Our data revealed not only genes "enriched" or differentially expressed in PA1 during fourth and fifth week of human development, but also 6927 genes newly identified to be expressed in human PA1. Many of these genes are involved in biosynthetic processes and have binding function and catalytic activity. We compared expression profiles of human genes with those of mouse homologs to look for genes more specific to human craniofacial development and found 766 genes expressed in human PA1, but not in mouse PA1. We also identified 1408 genes that were expressed in mouse as well as human PA1 and could be useful in creating mouse models for human conditions. We confirmed conservation of some human PA1 expression patterns in mouse embryonic samples with whole mount in situ hybridization and real-time RT-PCR. This comprehensive approach to expression profiling gives insights into the early development of the craniofacial region and provides markers for developmental structures and candidate genes, including SET and CCT3, for diseases such as orofacial clefting and micrognathia.

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