MOLECULAR-CLONING AND SEQUENCING OF THE CYTOSTATIC-G PROTEIN-ACTIVATED PROTEIN-KINASE PAK-I

The serine/threonine protein kinase PAK I ((p) under bar 21-(a) under bar ctivated protein (k) under bar inase), a ubiquitous multipotential protein kinase of 58-60 kDa, has been shown to have cytostatic proper ties. Data from our laboratory show that PAK I is highly active in ooc ytes and quiescent and serum starved cells, and injection of active PA K I into one blastomere of two-cell frog embryos inhibits cleavage of the injected blastomere. To clone the cDNA encoding PAK I, purified pe ptides from rabbit PAK I were sequenced, degenerate oligonucleotides w ere used to isolate PAK I clones from a rabbit spleen library, and the 5'-terminus was obtained by polymerase chain reaction. The entire cDN A sequence extends over 4471 nucleotides, with an open reading frame f or a protein of 524 residues and a 3'-noncoding region of 2826 nucleot ides. Clones with the same open reading frame but with 3'-noncoding re gions of 1055 and 2478 nucleotides were isolated, suggesting the gener ation of different transcripts by alternative termination of transcrip tion. The amino acid sequence of PAK I shows high homology to the pal- activated protein kinases from human placenta and rat brain and to yea st STE20. PAK I is activated by Cdc42(GTP). The PAK enzymes have been proposed to regulate the stress-activated protein kinase (also known a s the Jun kinase) signaling pathway (Coso, O. A., Chiariello, M., Yu, J.-C., Teramoto, H., Crespo, P., Xu, N., Miki, T., and Gutkind, J. S. (1995) Cell 81, 1137-1146; Minden, A., Lin, A., Claret, F.-X., Abo, A. , and Karin, M. (1995) Cell 81, 1147-1157).