SWM1, a developmentally regulated gene, is required for spore wall assembly in Saccharomyces cerevisiae

Meiosis in Saccharomyces cerevisiae is followed by encapsulation of haploid nuclei within multilayered spore walls. Formation of this spore-specific w all requires the coordinated activity of enzymes involved in the biosynthes is of its components. Completion of late events in the sporulation program, leading to spore wall formation, requires the SWM1 gene. SWM1 is expressed at low levels during vegetative growth but its transcription is strongly i nduced under sporulating conditions, with kinetics similar to those of midd le sporulation-specific genes. Homozygous swm1 Delta diploids proceed norma lly through both meiotic divisions but fail to produce mature asci. Consist ent with this finding, swm1 Delta mutant asci display enhanced sensitivity to enzymatic digestion and heat shack Deletion of SWM1 specifically affects the expression of mid-late and late sporulation-specific genes. All of the phenotypes observed are similar to those found far the deletion of SPS1 or SMK1, two putative components of a sporulation-specific MAP kinase cascade . However, epistasis analyses indicate that Swm1p does not form part of the Sps1p-Smk1p-MAP kinase pathway. We propose that Swm1p, a nuclear protein, would participate in a different signal transduction pathway that is also r equired for the coordination of the biochemical and morphological events oc curring during the last phase of the sporulation program.