CHARACTERIZATION OF A CDNA-ENCODING THE 55 KDA B-REGULATORY SUBUNIT OF ARABIDOPSIS PROTEIN PHOSPHATASE 2A

Type 2A serine/threonine protein phosphatases (PP2A) are key component s in the regulation of signal transduction and control of cell metabol ism. The activity of these protein phosphatases is modulated by regula tory subunits. While PP2A activity has been characterized in plants, l ittle is known about its regulation. We used the polymerase chain reac tion to amplify a segment of a cDNA encoding the B regulatory subunit of PP2A from Arabidopsis. The amplified DNA fragment of 372 nucleotide s was used as a probe to screen an Arabidopsis cDNA library and a full -length clone (AtB alpha) of 2.1 kbp was isolated. The predicted prote in encoded by AtB alpha is 43 to 46% identical and 53 to 56% similar t o its yeast and mammalian counterparts, and contains three unique regi ons of amino acid insertions not present in the animal B regulatory su bunit. Genomic Southern blots indicate the Arabidopsis genome contains at least two genes encoding the B regulatory subunit. In addition, ot her plant species also contain DNA sequences homologous to the B regul atory subunit, indicating that regulation of PP2A activity by the 55 k Da B regulatory subunit is probably ubiquitous in plants. Northern blo ts indicate the AtB alpha mRNA accumulates in all Arabidopsis tissues examined, suggesting the protein product of the AtB alpha gene perform s a basic housekeeping function in plant cells.