In eukaryotes, the principal nuclear import pathway is driven by the importin alpha/beta1 heterodimer. KapA, the Aspergillus nidulans importin alpha, is an essential protein. We generated a conditional allele, kapA31, mimicking the srp1-31 allele in Saccharomyces cerevisiae. KapA31 carries a Ser111Phe amino acid substitution which, at the restrictive temperature of 42 degrees C, reduces nuclear import of cargos containing classical nuclear-localization-sequences, cNLS. Using kapA31, we have demonstrated the role of the importin alpha in the nuclear accumulation of the light-dependent developmental regulator VeA. KapA have additional tasks in the cell, as reported for other members of the importin alpha family. KapA participates at different regulatory stages of asexual and sexual development, being required for the completion of both reproductive cycles with the formation of conidiospores and ascospores, respectively. Finally, KapA also mediates in different pathways of secondary metabolism having a dual role: positively for penicillin production and negatively for mycotoxin biosynthesis.