Nuclear import of Ho endonuclease utilizes two nuclear localization signals and four importins of the ribosomal import system

Anya Bakhrat, Keren Baranes, Oleg Krichevsky, Inna Rom, Gabriel Schlenstedt, Shmuel Pietrokovski, Dina Raveh

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Activity of Ho, the yeast mating switch endonuclease, is restricted to a narrow time window of the cell cycle. Ho is unstable and despite being a nuclear protein is exported to the cytoplasm for proteasomal degradation. We report here the molecular basis for the highly efficient nuclear import of Ho and the relation between its short half-life and passage through the nucleus. The Ho nuclear import machinery is functionally redundant, being based on two bipartite nuclear localization signals, recognized by four importins of the ribosomal import system. Ho degradation is regulated by the DNA damage response and Ho retained in the cytoplasm is stabilized, implying that Ho acquires its crucial degradation signals in the nucleus. Ho arose by domestication of a fungal VMA1 intein. A comparison of the primary sequences of Ho and fungal VMA1 inteins shows that the Ho nuclear localization signals are highly conserved in all Ho proteins, but are absent from VMA1 inteins. Thus adoption of a highly efficient import strategy occurred very early in the evolution of Ho. This may have been a crucial factor in establishment of homothallism in yeast, and a key event in the rise of the Saccharomyces sensu stricto.

Original languageEnglish
Pages (from-to)12218-12226
Number of pages9
JournalJournal of Biological Chemistry
Volume281
Issue number18
DOIs
StatePublished - 5 May 2006

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