The Aspergillus nidulans swoK1 mutant is defective in polarity maintenance when grown at restrictive temperature (38 degrees C). Upon germination, the mutant extends a primary germ tube that swells to an enlarged, non-uniform cell with pronounced wall thickenings. The mutant is fully restored to wild-type growth when transformed with a plasmid containing the AN5802.2 ORF as designated in The Broad Institute A. nidulans sequence database. Genetic mapping places swoK in the same region of chromosome I, as that occupied by An5802.2 on the physical map. swoK is predicted to encode a protein that contains an N-terminal RRM (RNA Recognition Motif) and a highly repetitive C-terminus with numerous RD/DR and RS/SR dipeptides. We hypothesize that SwoK participates in one of the known functions of SR proteins (those that contain SR/RS repeats): mRNA maturation through the spliceosome and or transport of mRNAs out of the nucleus to sites of protein translation.