A Zea mays Pollen cDNA Encoding a Putative Actin-Depolymerizing Factor

Microfilaments perform essential functions in eukaryotic cells, being responsible, in conjunction with other cytoskeletal elements, for the structural integrity of the cell and also for many of the cellular movements, including muscle contraction, cytokinesis, cytoplasmic streaming, and phagocytosis. The structural versatility of microfilaments is mediated by actin-binding proteins (Hartwig and Kwiatkowski, 1991). A group of small actin-binding proteins, the ADF group, has the ability to regulate actin polymerization and depolymerization. Proteins within the ADF group have similar properties and they include vertebrate ADF (Bamburg et al., 1980), or destrin (Moriyama et al., 1990), vertebrate and yeast cofilin (Nishida et al., 1984; Iida et al., 19931, starfish depactin (Mabuchi, 1981), and Acanthnmoeba actophorin (Cooper et al., 1986). Chemical cross-linking experiments, mutational analysis, and competition studies using synthetic peptides have demonstrated that the amino acid region from Trplo4 to Leu'" in pig cofilin is likely to be a multifunctional domain binding both phosphoinositides and actin (Yonezawa et al., 1991a, 1991b; Moriyama et al., 1992); the Lys114 plays a pivotal role in the actin-depolymerizing activity of cofilin (Moriyama et al., 1992). This amino acid region is highly conserved among the members of the ADF group. Recently, a lily anther preferentially expressed cDNA was isolated and sequenced by An and colleagues (Kim et al., 19931, and the deduced amino acid sequence showed significant homology to the proteins in the ADF group. In a similar study, we differentially screened a maize pollen cDNA library with radiolabeled shoot and pollen cDNA and isolated a pollen-abundant cDNA, ZmABPl. The nucleotide sequence of ZmABPl shows homology to the lily cDNA and to the members of the ADF group (Table I). ZmABPl was found to encode a protein of 139 amino acids. The deduced amino acid sequence shows 70% identity (97% similarity) with the lily sequence. A comparison of the maize sequence with the sequence of the members of