The SONB^NUP98 Nucleoporin Interacts With the NIMA Kinase in Aspergillus nidulans

Corresponding author: Stephen A. Osmani, Ohio State University, 804 Riffe Bldg., 496 W. 12th Ave., Columbus, OH 43210., osmani.2{at}osu.edu (E-mail)

Communicating editor: M. ZOLAN

The Aspergillus nidulans NIMA kinase is essential for mitotic entry. At restrictive temperature, temperature-sensitive nimA alleles arrest in G₂, before accumulation of NIMA in the nucleus. We performed a screen for extragenic suppressors of the nimA1 allele and isolated two cold-sensitive son (suppressor of nimA1) mutants. The sonA1 mutant encoded a nucleoporin that is a homolog of yeast Gle2/Rae1. We have now cloned SONB, a second nucleoporin genetically interacting with NIMA. sonB is essential and encodes a homolog of the human NUP98/NUP96 precursor. Similar to NUP98/NUP96, SONB^NUP98/NUP96 is autoproteolytically cleaved to generate SONB^NUP98 and SONB^NUP96. SONB^NUP98 localizes to the nuclear pore complex and contains a GLEBS domain (Gle2 binding sequence) that binds SONA^GLE2. A point mutation within the GLEBS domain of SONB1^NUP98 suppresses the temperature sensitivity of the nimA1 allele and compromises the physical interaction between SONA^GLE2 and SONB1^NUP98. The sonB1 mutation also causes sensitivity to hydroxyurea. We isolated the histone H2A-H2B gene pair as a copy-number suppressor of sonB1 cold sensitivity and hydroxyurea sensitivity. The data suggest that the nucleoporins SONA^GLE2 and SONB^NUP98 and the NIMA kinase interact and regulate nuclear accumulation of mitotic regulators to help promote mitosis.

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