A mutant in the essential gene shows phenotypic markers of apoptosis

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Abstract
We report the study of Kluyveromyces lactis cells expressing a truncated form of KlLSM4, a gene ortholog to LSM4 of Saccharomyces cerevisiae which encodes an essential protein involved in both pre-mRNA splicing and mRNA decapping. We had previously demonstrated that the first 72 amino acids of the K. lactis Lsm4p (KlLsm4Δp) can restore cell growth in both K. lactis and S. cerevisiae cells not expressing the endogenous protein. However, cells showed a remarkable loss of viability in stationary phase. Here we report that cells expressing KlLsm4Δp presented clear apoptotic markers such as chromatin condensation, DNA fragmentation, accumulation of reactive oxygen species, and showed increased sensitivity to different drugs. RNA analysis revealed that pre-mRNA splicing was almost normal while mRNA degradation was significantly delayed, pointing to this as the possible step responsible for the observed phenotypes.