| Citation | Distinguished for his work on the molecular genetics of yeast. His early work made substantial contributions to the study of the cell cycle in fission yeast, including the isolation and characterisation of cell cycle mutants and the first identification of a gene product (DNA ligase) in these mutants. His main contribution has been to the understanding of the intricate sequence of transcriptional regulation which occurs during the transitions of haploid homothallic spores into diploid cells and their subsequent behaviour. His results have produced important insights into the mechanism of mating type switching by showing how mating type genes regulate the expression of other genes and how the mating type genes are themselves regulated by the transposition of silent copies away from a silencer element. He demonstrated that the pedigree of mating type switching is due to the pattern of expression in the HO endonuclease gene which initiates the mating type gene conversion and which is expressed only in mother cells at a late stage of the Gl phase of the cell cycle. He discovered and characterised a transcription factor for the HO gene called SW15, which is distributed asymmetrically at cell division, and which explains why it is that only the mother cell and not the daughter can switch its mating type. Nasmyth has also made other major contributions to molecular biology. He was one of the first to demonstrate that gene expression can be regulated through specific control elements which are distant from the start of transcription and he has recently characterised a transcription factor, which is apparently involved in both activation and repression depending upon the context of its binding site. |