Related Experiment Videos
Tropomyosin is essential in yeast, yet the TPM1 and TPM2 products perform distinct functions
B Drees1, C Brown, B G Barrell
1Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853.
Abstract:
Sequence analysis of chromosome IX of Saccharomyces cerevisiae revealed an open reading frame of 166 residues, designated TPM2, having 64.5% sequence identity to TPM1, that encodes the major form of tropomyosin in yeast. Purification and characterization of Tpm2p revealed a protein with the characteristics of a bona fide tropomyosin; it is present in vivo at about one sixth the abundance of Tpm1p. Biochemical and sequence analysis indicates that Tpm2p spans four actin monomers along a filament, whereas Tpmlp spans five. Despite its shorter length, Tpm2p can compete with Tpm1p for binding to F-actin. Over-expression of Tpm2p in vivo alters the axial budding of haploids to a bipolar pattern, and this can be partially suppressed by co-over-expression of Tpm1p. This suggests distinct functions for the two tropomyosins, and indicates that the ratio between them is important for correct morphogenesis. Loss of Tpm2p has no detectable phenotype in otherwise wild type cells, but is lethal in combination with tpm1 delta. Over-expression of Tpm2p does not suppress the growth or cell surface targeting defects associated with tpm1 delta, so the two tropomyosins must perform an essential function, yet are not functionally interchangeable. S. cerevisiae therefore provides a simple system for the study of two tropomyosins having distinct yet overlapping functions.
Insights
Yeast tropomyosin Tpm2p, though less abundant than Tpm1p, binds actin filaments and influences cell shape. The ratio of these tropomyosins is crucial for yeast morphogenesis, highlighting distinct yet overlapping functions.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Saccharomyces cerevisiae possesses two tropomyosin isoforms, Tpm1p and Tpm2p.
- Tropomyosins are crucial actin-binding proteins involved in muscle and non-muscle cellular functions.
Purpose of the Study:
- To characterize the newly identified yeast tropomyosin, Tpm2p.
- To investigate the distinct and overlapping functions of Tpm1p and Tpm2p in yeast morphogenesis.
Main Methods:
- Sequence analysis of chromosome IX.
- Protein purification and characterization of Tpm2p.
- In vivo studies involving gene over-expression and deletion mutants.
Main Results:
- Tpm2p shares 64.5% sequence identity with Tpm1p and binds F-actin, spanning four actin monomers.
- Tpm2p is present at one-sixth the abundance of Tpm1p but can compete for actin binding.
- Over-expression of Tpm2p alters yeast budding patterns, suggesting distinct roles and importance of the Tpm1p/Tpm2p ratio for morphogenesis.
Conclusions:
- Tpm1p and Tpm2p have distinct yet overlapping functions essential for yeast cell viability and morphogenesis.
- The ratio between Tpm1p and Tpm2p is critical for proper cell shape and function.
- S. cerevisiae serves as a model system for studying tropomyosin functional diversity.