Fig. 8. Structure of SPW1 gene and the molecular analysis of spw1 mutations. (A) Genomic structure of the SPW1 gene. The SPW1 gene consists of seven exons and six introns. The length of introns are 101, 204, 173, 448, 2168 and 124 bp, respectively. In the spw1-1 mutant, the last base of third intron of G is mutated to A. In spw1-2, the first base of the fifth intron of G is changed to A. (B) Deduced cDNA and protein sequence of SPW1. Arrowheads indicate the position of introns. The MADS box is indicated by the thick line and the K-box by the thin line. The solid box indicates the two amino acid residues deleted in spw1-1. The dashed box shows the exon that is deleted in spw1-2. The genomic sequence is available at the GenBank (accession no. AF424549). (C) RNA blot analysis of the SPW1 transcript in spw1 mutants. 1 µg of poly(A) RNA from spw1 mutants and wild-type was subjected to gel electrophoresis and hybridization with an SPW1-specific probe. 1 kb-long SPW1 transcript was detected in the wild type as well as mutants, but with a lesser amount in mutants. Unspliced RNA was not detected in mutants. (D) The same blot was hybridized with the probe for ubiquitin genes (accession number AC103891). (E) SPW1 RT-PCR analysis of spw1 mutants. The amplification of the region between exon 1 and 6 showed that the spw1-2 mutation resulted in the deletion of an approximately 100 bp-long sequence from SPW1 mRNA.

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