The SONBNUP98 Nucleoporin Interacts With the NIMA Kinase in Aspergillus nidulans

Abstract

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.